Zombie Derby: Pixel Survival

Short Fuse Alex can be found in Level 5. Keep driving and you'll find him and the achievement will pop when you get back to the garage.

I found the Hangover, Tommy Kong and Short fuse Alex on level 5 (Every time I died, I got a new character on the level.

Short Fuse Alex is a zombie in an striped shirt rushing towards you holding a stick of dynamite and shows up in the fifth level (only after you've encountered and defeated The Hangover and Tommy Kong found in the same level). The game will highlight this "new enemy" to you the first time you encounter it. Simply shoot him and wait for the level to end, either by exploding your car, coming to a full stop or completing the level.