The Warlord (Ape/Yeti and Werewolf Transformations)

In issue 120 of this fantasy comic a villain named Redmond is rescued by a tribe of "snowmen," yetis who were once human until they entered a strange snowy valley:

 

By the next issue Redmond has also transformed. He escapes from the snowmen, but not before stealing their new cure to temporarily restore humanity:

In issue 122 Redmond turns back to normal...for now:

After transforming again (off-panel), Redmond wakes up human and crazy in the next issue:

Poor Redmond met his death later in the issue. Werewolf fans will be happy to know that one shows up in issue 47:

Idle Transformation (Werewolf, Yeti, Lizard and Chimpanzee Transformations)

 My thanks to Arenson for recommending this "max level" gameplay video from the mobile game Idle Transformation. It shows a man turning into a werewolf, yeti, lizard-man, mummy, and chimpanzee.

Futurama (Yeti transformation)

By Daymon.
Enjoy this clip from Futurama, wherein Professor Farnsworth gets transformed (and then further transformed) by yeti venom:

Phineas and Ferb (Yeti Transformation)

I learned of this video from the Shoe Burst tumblr--the scene is from the first episode of the fourth season. Evil Professor Doofenshmirtz turns himself into the Abominable Snowman (i.e. the yeti):

(In case you want to see his butt grow, the clip's here.)