Transformation Guild

The more you kill the more you turn into them, as you level up you gain more things that hurt your appearance but as you level higher and higher you get less and less affected by these flaws you find yourself with. This power is usually only gained by people who have been cursed with ravenous hunger or have been affected by the true polymorph spell or have been infected with Lycanthropy and were cured while in the middle of their transformation

Level 3: Beast Transformation

If you kill a creature that is a type of creature that you have a grimoire on and the CR is no higher than 1 above your character level you can turn into the creature using your stats besides for hp and languages. When you turn into a creature you use the statblock of the creature and if you die as that creature you turn back. The transformation lasts for 1 hour.

Level 3: The Beast Of Creation

You Can Make The Shapes Of Beasts You Kill To Use Some Of Their Power And Harness It.

Level 7: Mind of the beast

Through the transformation of turning into beasts you have become stronger with the transformation and now you find yourself able to turn into better creatures, you can now turn into creatures with a CR to a maximum of 6 above your level and you have 2 more uses of the transform ability and it lasts 5 hours, and you keep the ability to turn into the creature for 48 hours or 2 days instead of 20 hours. You can cast detect with this due to turning into mostly intelligent creatures

Level 10: Stolen Power

Steal power.   Whenever you attack a creature that has 100 hp or less you can use your bonus action to attack it again, and if the second attack hits you deal necrotic damage and it has life-steal  so you heal the amount of damage dealt and if the second attack kills it, you gain the transformation into that creature even if you don't have a grimoire on it you

Level 15: Arcane Transformation

When you turn into a creature made by magic such as summon beast, or summon celestial that you have killed lets you cast up to 6th level spells without needing material components, in addition you can pick 2 abilities to increase your damage, increase your defense, or increase your movement

Beast Breaker

Siege Monster  When transformed into a creature that has the size of large or bigger you deal 2 times the damage to objects and structures (including constructs) 

Break bones When you hit a creature with bludgeoning damage and deal 75+ damage you can break their bones, meaning that if you hit them on the arm and break it, they cannot attack with that arm

Beast Hide

You gain a +2 ac when taking this, the +2 carries even when you go into your beast transformation

Maim

Maim as an action you can maim someone by cutting off a limb of theirs that will permanently damage them

Speed Of The Tiger, Bite Of The Shark

You gain a +20 to your walking speed 

Transformed Onslaught

While in transformation you have 3 attacks and if you have something such as Fire Breath from the adult red dragon, you can use those instead of attacks no matter what it says, so if there is an ability that would make it so you forfeit all other attacks you can do the same amount of attacks you would normally have as if you did a gore attack

Level 18: Beast Of Power

Beastly power as an action you can draw the power from a living creature with no more than 200 hp left and make a melee attack against the creature and deal double damage, or on a Natural 20 you instantly kill the creature however you can only use this while transformed