The Half-Breeds: Half-Ogre, Half-Rakshasa, Half-Minotaur, and Half-Dwarf

Just like half-elves and demontouched, there has been no definitive explanation on how they are born, and half-breeds sometimes spontaneously appear in the Dragon Empire, although not always to the delight of their parents and communities.

Simple Reflavoring

For GMs who want a quick and dirty conversion that doesn't require the features below, feel free to reflavor the Dwarf, Dark Elf or Half-Orc into either the Half-Ogre/Half-Giant or the Half-Minotaur, the Dwarf into the Mul, , and the Half-Elf as the Half-Rakshasa.  For those who want more distinct mechanical differences, see below.

Also, in keeping with the theme, the following half-breeds already exist in 13th Age: Half-Dragon (Dragonspawn), Half-Fiend (Demontouched), Half-Celestial (Aasimar) and Half-Drow (Half-Elf).

Half-Ogre/Half-Giant

+2 Strength OR +2 Constitution
Ogrish Toughness: Once per battle as a quick action, you can spend a recovery to gain temporary hit points equal to the rolled result.

(Champion Feat): One battle per day when you trigger Ogrish Toughness, add 1d6 per level damage whenever you miss with a melee basic attack.

GM Note: Notice that the Half-Ogre/Half-Giant and the Earthborn/Stone-Touched both share the same benefits for their racial power.  If you wish to use both races, but want to make the Half-Ogre/Half-Giant different, replace the Half-Ogre/Half-Giant's Ogrish Toughness with the following racial power (racial feat stays the same):

Monstrous Strength: Once per scene when making a Strength-related check, you can choose to lower the check's DC by an amount equal to your Strength plus the current escalation die.  You can do this even after finding out the result of your check.

The reason why I didn't want to make this the default racial power for Half-Ogres/Half-Giants would be because it doesn't feel "right" for me to grant this strength-specific power to them.  But if that works for your campaign, then so be it.

Half-Rakshasa

+2 Intelligence OR +2 Charisma
Shapechange: Once per scene as a standard action, you can change your form to that of any humanoid. While shapechanged, you retain all of your statistics, and you can turn back to your own form as a standard action, although being reduced to 0 HP also forcibly turns you back to your own form.
It takes a successful hard save for nearby creatures to notice that there's something... different, about you, and other factors (like trying to mimic a particular person, acting out of character, or trying to look discreet) that could make the save normal, easy, or impossible (GM discretion).

(Champion Feat): Whenever a creature trying to determine if you're what you look like rolls a 5 or lower on their saving throw, you can change it to a natural 1 and improvise on how their attempt to see who you really are actually works in your favor.  Perhaps they expose useful information about the creature you're trying to appear as, or they can even become friendly to you (until they find out who you really are).  The better the storytelling improv, the better the result, though if the GM thinks your suggestion is going too far, they can enforce a smaller version of your improv or call for an unmodified d20 roll (high roll likely gets what you want).

Note: This race easily works for Changelings and the like.

Half-Minotaur

+2 Strength OR +2 Wisdom
Goring Charge: During your turn, when you make a melee attack a staggered enemy you were not engaged with at the start of your turn, add damage equal to your Strength modifier on a hit.  Increase this damage to twice your Strength modifier at level 5, and three times your Strength modifier at level 8.

(Champion Feat): You also pop the enemy free from any other creature they're engaged with except you, and they have a -2 penalty to disengage checks against you until the end of their next turn.

GM Note: This is the only race I would design to overlap with the Barbarian's Slayer talent, and generally benefit from a charge-like ability.  This is due to the iconic nature of the Minotaur's goring charge.

Half-Dwarf

+2 Strength OR +2 Constitution
Half-Dwarf Endurance: Once per scene you are able to perform strenuous tasks for longer periods of time.  This will usually come in the form of lower DCs for one Constitution check, but may also involve other activities that can put significant strain on your character, such as heavy lifting or hurried tome-scribing.  Discuss with your GM how this feature works during character creation.

(Champion Feat): Increase the number of recoveries that you have by one, and the first time you rally each battle can be done as a quick action instead of a standard action.

GM Note: This is a rather tricky thing to resolve mechanically, but for those who are more familiar with D&D's Mul race might have an easier time with this racial feature.

Forestfolk (3.5E, 4E)

The Wild Wood and other forests is home to a variety of unusual creatures.  Some are considered to be related to the Elves -- indeed, a few of these rare folk are also called "Fey" or fairy folk.

Three types of the rare fey will be discussed here: Springlings, Pixies, and Satyrs.

Springlings are a collection of plant-like creatures that each have developed a way to survive in the world.  Some are called "Hamadryads" by other races because of their resemblance to the beautiful dryads of legend, while the more fungi-like are often called "Myconids".  Others even call themselves Wilden because of their pride in being creatures of the wild, but regardless they are all plant-like humanoids each with his or her own way of doing things.

Pixies are a curious lot: they're extremely tiny creatures, smaller than even the gnomes and halflings, and are often helpless when tackling things individually.  However, once in awhile -- and for some odd reason it tends to be the pixie with the worst case of dandruff (you really wouldn't want to imagine the alternatives to explaining how "pixie dust" is made and extracted) -- exceptionally adventurous and capable pixies separate from the swarm and wander off into the world.

Satyrs are a fun-loving group of goat people, who are often seen with an unusual set of windpipes as a musical instrument.  If any satyr comes out of the forest and into the city, luck is sure to follow.

... just don't expect that luck to be the good sort.

Simple Reflavoring

For GMs who want a quick and dirty conversion that doesn't require the features below, feel free to reflavor Dwarves as Springlings, Gnomes as Pixies, and Demonspawns/Tieflings as Satyrs. For those who want more distinct mechanical differences, see below.

Springling

+2 CON or CHA
Biotal Defense: Once per battle as a reaction to a missed melee attack, make a check with your highest attribute against the nearby opponent that has the highest PD.  On a success, you can cause one engaged opponent to be dazed until the end of their next turn.
Author's Note: Please replace the word "biotal" with the type of defense your springling character uses.  For instance, Pheromone defense would likely involve charming enemies with enticing scents, while Thorn defense would likely involve either discouraging or hindering the enemy's attacks with the sudden appearance of thorns.

(Adventurer Feat): You can expend the use of your Biotal Defense to gain a +2 to any Charisma-based check, as long as it is appropriate to the method you normally use as defense.
(Champion Feat): Once per day you can affect each nearby enemy, instead of one engaged opponent.  At the end of a fight, you can either roll a 16+ or spend a recovery to regain the use of this feat.

Pixies

+2 DEX or CHA
Pixie Dust: Once per battle you can cause yourself or a nearby ally to fly to a nearby location as a move action.

(Champion Feat): You can instead expend the use of your Pixie Dust as a standard action to manipulate light immediately around you for a round.  Normally this could either render you completely invisible for a round, or amplify the glitter of your pixie dust to create an astounding burst of light that would have you make a Charisma-based attack versus each engaged enemy and cause them to become dazed, but you'd probably want to discuss the effects and implications with the GM ahead of time as well.

Author's Note: If the GM is cool with it, this feat will allow you to treat Pixie Dust as a spell, allowing you to use this as part of a ritual if you are able to cast rituals (either by taking the wizard or cleric class, or taking the ritual caster feat).

Small: Pixies have a +2 AC bonus against opportunity attacks.

Author's Note: Even though they may appear to be smaller than gnomes or halflings, I personally see no reason why their basic mechanical benefits involving size should go beyond that of other small folk.  In fact, the mechanics that 4E introduce basically make them mechanically small (more or less), even though they were written as Size: Tiny.  I also didn't bother writing down the technicalities involving pixie flight and what not, under the assumption that it's the logical explanation for pixies being able to keep up with the rest of the group in terms of movement (much like how gnomes and halflings in 13th Age aren't actually penalized movement-wise for being small).

Satyr

+2 CON or DEX
Satyr's Charm: Whenever you make a Charisma check involving charming, deceiving or scaring an opponent, roll a die to determine if you can re-roll the result. If your roll is equal to or lower than the escalation die, you can roll that Charisma check a second time and choose whichever result you want.
After making the Charisma check, roll a d6.  Each time you get to re-roll your Charisma check, the die you roll increases by one step in the following progression: d6, d8, d10, d12, d20. If you get to re-roll your Charisma check after the d20, you can no longer re-roll your Charisma check for the remainder of that battle.

(Champion Feat): You can roll two of the dice used for Satyr's Charm (e.g. 2d6 instead of 1d6) and pick either result.

Author's Note: Rather than explicitly give the Satyr a 1/battle dazing ability, I decided that everyone who wanted to bluff or intimidate an enemy into a compromising position should be able to do so, it's just that Satyrs simply do it better using their music and their natural charm.

Genasi (4E, 3.5E)

The Genasi are a collection of near-human races that are said to be a result of the Archmage's experiments with the elements**.  Also called Element-Touched, or sometimes Elementborn, the common thing going on with them is that an element -- or for hybrids (called Para-Genasi), a multitude of elements -- not only affects their appearance, but also their personalities, to some degree:  Air-Touched tend to be as light-hearted and fickle as the wind, Earthborn are as stubborn and blunt as stone, Fire-Touched tend to be as rash and hot-headed as an blazing campfire, and Waterborn tend to be gentle and calm like a stream.  That doesn't mean that you can't have Air-Touched that act like a furious gale, Earthborn that are as shifty as the sand, Fire-Touched as gentle and warm as a candle's flame, and Waterborn with the wrath of a flood, but people tend to be a bit stereotypical on the matter.

Genasi can often be found in areas where the element they're associated with have the greatest influence (e.g. Waterborn in rainforests, Fire-Touched near volcanoes and hellholes, Earthborn in caverns and crevasses along the mountains, and Wind-Touched in arid deserts and rocky mountains where the wind blows strongest).

** plane(s) may or may not be involved with these experiments.

Simple Reflavoring

For GMs who want a quick and dirty conversion that doesn't require the features below, feel free to reflavor the Dragonspawn into the Fire Genasi, the Dwarf into the Earth Genasi, the Wood Elf as the Wind Genasi, and High Elves as the Water Genasi.  For those who want more distinct mechanical differences, see below.

Common Genasi Racial Feats

(Champion Feat): You gain resistance to the element you're associated with equal to 1 + half your level.  If your mix of two elements, the resistance you gain to both elements is one third your level. Any more, and you're getting only a fifth of your level in resistance, or none at all if the GM would consider your bloodline too thin to benefit from this feat.

GM Note: If you think the bloodline is too thin for the PC to benefit from it, don't let him get this at all (if he already took it, allow him to retrain it out without any hassles); also, while it's tempting to add a flaw with this feat that would render PCs vulnerable to damage of an opposing element, run that first with the players and see if they're alright with it (and maybe downgrade it to an adventurer feat if the rest of the group is fine with the flaw), otherwise assume that because the PCs are exceptional for their race, they have no downsides to taking this feat.

Air-Touched/Windborn

+2 DEX or CHA

Wind Dancer: Once per battle, you can roll 2d20 for any mobility-related stunt (such as leaping over pits) and pick either one as a result.

(Champion Feat): Once per battle as an interrupt, when a ranged attack is made against you, you can gain a +4 to AC and PD for that attack.

Earthborn/Stone-Touched

+2 STR or CON

Stone's Endurance: Once per battle as a quick action, you can spend a recovery to roll your recovery dice and gain temporary hit points equal to the result.

(Champion Feat): Once per day as a quick action, you gain resistance to normal weapons equal to your level until the end of your next turn.

Author's Note: I recommend that GMs who wish to introduce 4E Half-Giants/Goliaths in their campaign take this Genasi sub-race and reflavor them into Goliaths.

Fire-Touched/Flameborn

+2 DEX or INT

Burning Vengeance: Once per battle as a free action after taking damage from a melee attack, deal fire damage equal to your level to the attacker.  This damage increases to twice your level at champion tier, and thrice your level at epic tier.

(Champion Feat): Each engaged creature takes damage from this ability, instead of just the attacker.

Waterborn/Water-Touched

+2 DEX or WIS

Gentle Flow: Once per battle, you can pop free from any opponent as part of a move action and roll a normal save to avoid one attempt to engage you during your movement.

(Champion Feat): Once per day as a quick action, you can cause either yourself or an ally engaged with you to either spend a recovery or make a save against a save ends effect (but not both).

Stormborn and other Para-Genasi

+2 in any stat

Born of the Elements: Choose one of the racial powers associated with your parent Genasi races.  You get that power. For example, a Stormborn is the child of a Wind-Touched and a Waterborn, so as a Stormborn you gain either Wind Dancer and Gentle Flow, but not both.  Feel free to refluff the selected racial power to match the desired "hybrid" element (e.g. Stormbringer would be a refluffed Wind Dancer that is accompanied by peals of thunder and perhaps some rain water too, instead of just a gust of wind).

(Champion Feat): Once per day as a quick action, as long as you are able to use the racial power you've chosen, you can temporarily switch to a different racial power and use that power.  This feat will allow you access to the feats of your second heritage's power.

Author's Note: The Champion feat basically allows you to switch racial powers, but does not allow you to use two racial powers in the same battle.