Title changed to reflect true nature of the thread. It's still sorta shameless though.

Curious to know how your Sprite will look like after evolution? Maybe curious about which Ultimates give what appearances? Or trying to build an aesthetic sprite and want to know which ultimate to get which appearance?
Or maybe you want information on skills and more Sprite stuff?

Look no further!
Note AGAIN: Please look at the specific ultimate part pictures, linked to the skills, before looking at the final forms before asking "Then what gives what?".

Drakon Evolutions
Drakon Firebolt Ultimates (Ears/Horn)
Drakon Flame Barrier Ultimates (Spikes/Beard)
Drakon Firestorm Ultimates (Wings/Arms)
2 possible final Drakon forms

Seraphynx Evolutions
Seraphynx Ray of Light Ultimates (Forehead)
Seraphynx Heart Attack Ultimates (Halo/Arms)
Seraphynx Angelic Aura Ultimates (Tail)
2 possible final Seraphynx forms

Maskeraith Evolutions
Maskeraith Caustic Quills Ultimates (Wing-Ears/Arms)
Maskeraith Shadow Cloak Ultimates (Horns)
Maskeraith Hexing Haze Ultimates (Mask)
2 possible final Maskeraith forms

The appearances for each of the 3 ultimates are then combined together to get your final form. If you looked at the Final Form first and want to know which skills determine which part, go click the links for the specific skills.

Some information on Ultimate skills:
At level 89 after full heating, you need to use an Ultimate Evo Catalyst to level up and in doing so you get to pick one of two ultimate skill paths (Read here) for your FIRST skill, and first skill only. At level 94 after full heating, you use another Ultimate Evo Catalyst again to level up and pick an ultimate for your SECOND skill, and finally at Level 99 after full heating you get to pick an ultimate for your THIRD and final skill and then it reaches level 100.
New information: Ultimates are ENTIRELY OPTIONAL and have to be picked through the individual Skill tabs. You can now have a level 100 winged Drakon without any beards or spikes if that is your wish! However, you still need an Ultimate Evo Catalyst to level up at those levels. Thanks Zevier.

Drakon's skills

Firebolt: Fires an orange explosive fireball. Slight knockback on impact, with a chance to set enemies on fire.
Possible augments: Focus: Cooldown reduction (17s > 16s > 15s > 14s), Impact: Damage increase, Extra Crispy: Increases fire strength and chance, explosion radius increase. Each strength of Extra Crispy seems to visually increase the size of Firebolt.
Concussive Firebolt: Firebolt changes from orange to red and has a white star similar to a stun gun's charge. On explosion has sparkles with chance of stun.
Meteoric Firebolt: Firebolt becomes a large blue flame fireball. Explosion has a blue flame effect with slightly greater knockback and bigger explosion radius (increases to about 4x4-5x5 radius!)
Harness cooldown (at max Focus): Advanced: 13s, Elite: 12s

Flame Barrier: Surrounds you with 2 orange fire orbs that damages targets without flinching them and has a chance to burn them upon hitting. During the duration of Flame Barrier, defense is temporarily increased.
Possible Augments: Focus: Cooldown reduction (42s > 40s > 38s > 36s), High Heat: Increases the damage of orbs and chance to set enemies on fire, Heavy Smoke: Increases the defense boost and duration of the orbs, to a maximum of 8 seconds.
Scorching Barrier: Orbs become red and there are now three orbs orbiting you, potentially increasing damage potential.
Backfire Barrier: Orbs become blue flame orbs. Upon execution for 1-2 seconds a very noticeable speed boost is given. Does not last the whole duration.
Harness cooldown (at max Focus): Advanced: 34s, Elite: 32s

Firestorm: Creates a field of fire about 3x3 square range in front of you. Deals no damage and acts like an Ash of Agni, with a chance to burn any target that wanders in.
Possible Augments: Focus: Cooldown reduction (60s > 55s > 50s > 45s), Fire Alarm: increases the duration and size of the fire field, to a maximum size of 3x6 tiles forward and lasting 6seconds, Extra Crispy: Increases the strength of the fire inflicted and the chance of inflicting fire.
Frenzied Firestorm: Seems to have bigger aesthetic flame effects. Upon an enemy entering the fire field, high chance to apply 5 seconds of attack damage and attack speed boost. May be reapplied by other enemies wandering in, but does not go above 5 seconds per buff.
Explosive Firestorm: In addition to normal firestorm effects, tiny explosions happen throughout the entire duration of the storm and each explosion deals about half the damage of a fire tick, but hits about 10+ times should an enemy be inside the storm (such as being trapped in a vortex)
Harness cooldown (at max Focus): Advanced 42s, Elite 40s

Seraphynx's skills

Ray of Light: Fires a laser that has knockback and repetitively hits enemies for about 4-5times before they become immune to it for 1-2seconds. If they are still within range after immunity wears off they take damage again.
Possible augments: Focus: Cooldown reduction (24s > 22s > 20s > 18s), Magnify: Increases the length of the beam and its damage, Enduring Light: Increases the duration of the laser beam (2s without upgrade, 8-10s after max upgrade)
Dazzling Light Ray: The beam has a graphical twirling energy beam around it, does extra damage to undeads and fiends.
Disintegration Ray: The beam becomes a cyan-blue color and inflicts a debuff "status effect" that reduces enemies' defense not unlike poison, but can stack with poison's debuff.
Harness cooldown (at max Focus): Advanced 17s, Elite 16s

Heart Attack: Releases a single pulse indicated by a heart shape rune on the ground shortly after activating, which enchants enemies indicated by a red aura. Seems to increase the chance of a heart dropping and potentially increasing the number of hearts dropped by an enchanted enemy.
Possible Augments: Focus: Cooldown reduction (60s > 55s > 50s > 45s), Extra Hearty: Increases the chance of hearts/extra hearts dropping and the duration of the enchant, Wide Embrace: Increases the radius of the rune
Iron Heart Attack: Enchanted Targets have a chance to drop defense orbs. While not fully tested, one orb can grant 14-60 seconds of defense boost similar to the effect from Flame Barrier. The total defenses stack too!
Violent Heart Attack: Corpses of enemies affected by Violent Heart Attack will explode a short while after death, releasing a shower of heart-shaped visual effects. The explosions deal no damage (unknown whether this is a bug or intentional) but will damage/break blocks and/or knock aside enemies in a small radius, possibly 1-2 squares. Thanks to Concealrise.
Harness cooldown (at max Focus): Advanced 42s, Elite 40s

Angelic Aura: A yellow dome shield that completely shields you from damage without affecting movement or causing flinching, allowing you to walk on spikes and traps as well (although it breaks rather quickly). Can also shield teammates inside the radius.
Possible augments: Focus: Reduces Cooldown (60s > 55s > 50s > 45s), Protection: Increases the protection power of the shield, allowing it to take more damage before shattering, Cover: Increases the size of the shield and how long the shield lasts should it not break before dissipating.
Seraphic Aura: Blue dome shield with energy waves and "wings" graphic on the sides. Knights standing within it get noticeably faster shield regeneration rate.
Valkyrian Aura: Orange dome surrounded by energy waves. Makes all charge times Maximum! regardless of how much ctr was on it before, and does not go above Maximum!.
Harness cooldown (at max Focus): Advanced 42s, Elite 40s

Maskeraith's skills

Caustic Quills: Fires a bunch of toxic quills with a relatively high chance of poison on impact with an enemy, but does no damage. After impact, quills stick to the enemy and break off after taking damage from any source (even being healed by an enemy while poisoned!) and deal damage. Seems to have a maximum limit of 4(?) quills that can stick to an enemy.
Possible augments: Focus: Reduces Cooldown (24s > 22s > 20s > 18s), Venom: Increases the strength of the poison, Bristle: Increases the number of quills fired and the duration they stick to an enemy, lasting about 9 seconds at max upgrade and firing 11 at max upgrade. Each strength of Venom visually increases the size of quills and eventually turns it from purple to green.
Vengeful Quills: In addition to the normal effects, upon hitting an enemy, a new quill spawns randomly at another target. Quills become golden, spawned quills are green.
Virulent Quills: In addition to normal effects, upon detonation of the quill there is a random chance of it exploding and poisoning things within the blast radius similar to a haze bomb. Thanks to Venomousbiohazard.
Harness cooldown (at max Focus): Advanced 17s, Elite 16s

Shadow Cloak: Like a Recon cloak, but enemies can't detect you. Provides a defense buff while active, useful if you get attacked or damaged accidentally. Taking damage, dashing, charging a weapon or attacking will cancel the cloak.
Possible augments: Focus: Reduces Cooldown (60s > 55s > 50s > 45s), Dark Veil: Increases the defensive buff of the Shadow Cloak, Enduring Night: Increases the duration in which Shadow Cloak lasts, to a maximum of 15 seconds.
Deadly Shadow Cloak: In addition to normal buffs, a noticeable attack damage and an attack speed bonus is applied. Upon termination of cloak, all buffs are lost, but a 2 seconds attack damage and attack speed buff is applied after termination.
Vengeful Shadow Cloak: In addition to the normal cloak, upon disruption of the cloak, such as cancelling it with an attack or being damaged, a small graphical explosion occurs. Deals no damage but has a chance to stun enemies.
Harness cooldown (at max Focus): Advanced 42s, Elite 40s

Hexing Haze: Creates a purple miasma haze of a 6x6 squares area around you that inflicts a status condition called Hex on enemies. Hex lasts 3 seconds and "detonates" afterwards, dealing damage upon the end of it. Hex duration does not increase after infliction, but upon termination enemies can be inflicted again, usually up to two times during a single use. Inflicting hex on enemies seems to increase the duration of the haze by a small amount, with the haze lasting 5 seconds on average alone.
Possible augments: Focus: Reduces Cooldown (60s > 55s > 50s > 45s), No Mercy:: Increases the damage dealt by the Hex, Plentiful Pain: Increases the additional duration gained by inflicted enemies with Hex.
Haunted Haze: Same effects, but should an enemy die from the hex explosion, it releases a purple orb that does very minor damage with an explosion radius of one block. Damage is roughly the same as initial detonation of a Vortex bomb, which is about 5-7 damage in Tier 3.
Chaotic Haze: Haze turns a greenish-white color similar to Haunted aura(?), upon hexing a target (?) there is a chance a random status will apply, including Stun, Shock, Curse, Fire, Freeze and Poison (?).
Harness cooldown (at max Focus): Advanced 42s, Elite 40s

Information on Catalysts:
You need the 2* Catalyst after fully heating level 14 to evolve into level 15, the 4* catalyst after fully heating level 49 to evolve into level 50. You need one Ultimate Evo Catalyst at level 89 after fully heating to evolve into level 90 and get the Ultimate Skill for your first skill (Firebolt, Ray of Light, Caustic Quills depending on which sprite), then another Ultimate Evo Catalyst at level 94 after fully heating to get the Ultimate for your second skill (Flame Shield, Heart Attack, Shadow Cloak) and finally one last ultimate evo catalyst at level 99 after fully heating to get the Ultimate for your final skill (Firestorm, Angelic Aura, Hexing Haze).

Pet food information:
You can feed your pet ANY material, from 0 to 5*. From 0* pet, one flame soul could get it to almost full, just add a 3* mat and it's ready to level up. For most levels (except levels before evolutions) you could feed it any mat and it will only require it's favored food AFTER it is fully heated to level up (just like fire crystals!). Take note however that for every appropriate star mat, the favored food will give more- for example if your sprite's favored food is a 2* Divine dust, a 2* mat like blast powder will give less than a 2* Divine dust, but a 5* flame soul will still give more heat.
Starting from level 50 onwards, the favored food will ALWAYS give more than any other 5* mat.

Regarding Pet Star Levels and viability:
Now many current players are bound to be playing something of their own level, be it back to grinding Firestorm Citadel for Vanguards or perhaps the Royal Jelly Palace for Defenders. One thing to note about when you first get your pet is that it starts as a 0* pet, akin to your proto stuff. It is viable in T1, but bring it to any tier outside and any damage-based skills lose a lot of their efficiency. For example, a Drakon firebolt at level 1 might do about 7 damage to a T3 enemy, but at level 50 it can do 161 damage to a T3 enemy.
A pet is 0* from level 1-4, 1* from 5-14, 2* from 15-29, 3* from 30-49, 4* from 50-74, and 5* from level 75 onwards. Their damage potential scales with their star level, so if you think your sprite is too weak, chances are it's not at the appropriate tier for its level.

If any information is wrong or if you have anything more to add (I only have a level 43 Drakon as of writing anyway), please post below.

Thanks to Devilabyssbreaker for sharing some information. (Cool level 100 Drakon!)
Thanks to Zevier for pointing out Ultimates are optional.
Thanks to many others, including Furynator, Tdlob, Goldeneman, Produkt, Fehzor and more for information regarding ultimate skills.