Honestly I'm in the opposite boat. I've got a bunch of ideas for skills but am brand new to the modding scene. Struggle bussing my way towards learning the Divinity 2 Engine.

Here's some ideas -
Could have the forms either grant a bunch of strength, or grant strength based on (polymorph / summoning / whatever the mainstat is for these) skill level, or swap Int with STR for duration. In any case most should give bonus to an offensive stat.

Bear Form -
small movement penalty, small buff to armor, large vitality buff
Grants "Swipe" skill - scales w/ STR, it's a cleave like Cripple
Grants "Thick Fur?" skill - Restores Armor/Magic Armor to self (similar to the shield skill)

Wolf Form -
small movement buff, normal HP/armor
Grants Guerrilla talent
Grants "Throat Bite" skill - scales with STR, applies Suffocation and Bleeding to one target
Grants "Stalk" skill - 3 turn invis, slower movespeed while invis.

Crocodile Form -
normal speed, large armor buff, normal HP
Grants large bonus to preservance
Grants "Snap/chomp?" skill - scales w/ STR, High Dmg & applies Cripple to one target.

Bunny form -
large movement buff, normal Armor, small vitality penalty,
Grants dodge chance
Grants Duck Duck Goose talent
Grants "Hop" skill - Movement skill like tactical retreat

Condor form -
normal speed/hp/armor,
Grants flying for the duration
Grants Favorable Winds Aura for duration
Grants "Eye Rake" skill - scales w/ STR, hits twice and applies Blind to one target. (resisted by physical armor).

Just some ideas. What do you think?