FIRE BREATH: Transform in a Draconid demon to breath fire in AoE cone in front of you. You place a DoT on enemies.
FEAR PERSONIFICATION: Transform yourself in a Scarecrow for 5 seconds and creates and AoE made of 1000 crowns around you that fears everyone who touches the aura. Increases your movement speed.
CHAOS AURA: Transform yourself in a Chaotic creature, like a void elemental or something, damaging all enemies "1000" each second for 5 seconds.
MONSTROUS CHARGE: Transform yourself in a monstrous minotaurus charging and damaging all enemies in your way
CHAOS EXPLOSION: Release all inner chaos to create a explosion that damages for 3000 all enemies around you
SOUL DEVOURER: Transform yourself in a giant soul devourer to eat part of your target soul to heal yourself for "2000" and increase your damage in 20% for 10 seconds
DEMONIC PULL: Transform your arm in an octopus arm with eyes (lol) to pull 1 enemy to you, the 2nd use you transform yourself in the octopus monster to pull a maximum of 10 enemies around you in a range of 10 meters
METEORIC LANDING: Transform yourself in a winged bid demon to fly and increase your movement speed, 2nd use, you land stunning and damaging all enemies on the AoE
MONSTROUS BITE: Transform yourself in monstrous demonic dog to bite your enemy doing 1000 damage and causing him to bleed for 200 each second for 5 seconds.
These are just some ideas, this should be complemented with some no transformation skills, but those are the easy ones.