Zombie Yeti

The Zombie Yeti is a rare zombie that appears for the first time in the Fog level 4-10 (although it it does not technically contain any Fog) after playing Adventure Mode through at least one time. If the player doesn't kill it in time, it will run away, but if it is killed, it drops 5 diamonds (four in later encounters) and from then on randomly appear in other levels, although it will not be shown in the seed-choosing menu. It will also remain in level 4-10.

Overview
Absorbs 75 Normal Damage Shots. Appearance Changes after 45 Normal Damage Shots before dying at 75 Normal Damage Shots.

Suburban Almanac entry
 Zombie Yeti  A rare and curious creature. Toughness: high Special: runs away after a short while Little is known about the Zombie Yeti other than his name, birth date, social security number, educational history, past work experience and sandwich preference (roast beef and Swiss).

Strategy
Just do whatever you do to kill Buckethead Zombies. If it tries to run away, it can be stopped by planting a Pumpkin in its path (or other defensive plants during later levels). If that proves insufficient, plants capable of firing backwards can be planted inside.

Trivia

 * In the Mini-game Big Trouble Little Zombie the small version of this zombie can appear but does not drop diamonds.
 * There's a chance that you may see two Zombie Yetis in one level.
 * The Achievement Cryptozombologist is unlocked by seeing it.