darkSpyro

This is every alter ego I have so far, 26 in total.

Air:
Buttered Pop Thorn
Gourmet Gusto

Life:
Autumn Stump Smash
Builda Grilla Drilla
Fireworks Zook
Frosted Food Fight

Undead:
Fortune Funny Bone
Grill Master Chop Chop
Hallows' Eve Hex
Skeletal Cynder
Snowler Brawl

Earth:
Birthday Bash
Rocky Egg Roll
Sundae Slobber Tooth

Fire:
Cupid Flameslinger
Flip Flop Fryno

Water:
Holiday Wash Buckler
Marry Snap Shot
Surfer Slam Bam

Magic:
Buddy Wrecking Ball
Charmig Cobra Cadabra
Hoppity Pop Fizz
Mystic Star Strike

Tech:
Knockout Jawbreaker
Lucky Boomer
New Year's Eve Countdown

Light:

Dark:

There's also Admiral Thumpback, though I'm not quite sure he qualifies as an alter ego.

There's also Gnarly Tree Rex, though I'm not quite sure he qualifies as an alter ego either.

I would Label Admiral Thumpback as an Alter ego

I agree with Admiral Thumpback being an Alter ego - he's a variant that only exists within Lost Islands.

Gnarly Tree Rex though is a regular variant - I have the physical version of him.

Admiral Thumpback is considered an alter ego. He, Holiday Wash Buckler, and Frosted Food Fight were the only ones not available as a monthly well grand prize. I'm not sure if they were included as top prizes when they would put alter egos in the well, though. Admiral Thumpback was purchasable by kudos. I had assumed that was still the case, but I bought him when he came out, so I can't say, for sure. I got Holiday Wash Buckler for having Battlegrounds (though they eventually offered him for free on Christmas Day), and Frosted Food Fight was just a freebie (I believe for the launch of Trap Team in Lost Islands).

Gnarly Tree Rex is just a variant, as he has a physical figure.