Hey there! You probably aren't working on this mutation anymore (or it isn't top of your priorities), but I wanted to suggest new ideas for infected types if you ever wanted to make it more challenging.

Mighty Tank (1000HP) - A tiny-sized tank that runs extremely fast and can launch players with a single punch. You know what they say about small packages...

The Slender (200HP) - A smoker that takes the appearance of a long, sleek prop, like a pole or a tree. You'll have to double-check your eyes.

Bounty Hunter (300HP) - A charger who has infinite sprint capacity and full intentions to hunt you down. Also, he might've been smart in his previous life because he uses his uneven weight to turn while charging.

VIP (800HP) - A witch that must've been famous in her past life, thus causing an immediate swarm of commons (and riot guards) to spawn when she's disturbed.

Witchzard (650HP) - This witch has learned magic...whenever she receives damage, she can teleport. She also uses magic spells to spew explosives at the survivors.

The Claw (10000HP) - A superbly strong witch that runs at a quarter speed, but is built stronger than any infected. She's also easier to aggravate from afar, so prepare for a long-winded chase through the stage.

The Fat Kid (500HP) - A boomer/tank mixup. This boomer now runs faster, throws up more, and hits as hard as a tank. You should've never told him the helicopter was made of chocolate.

Familiar..Foe (??HP) - A witch that disguises herself as a special infected. Is that spitter planning a nice shot, or did the witch really let herself go? Only one way to find out...

Pit Crew (250HP) - Sedan Man's cooler, albeit more rare cousin. This race car acts similarly to the Sedan Man, except upon death, it releases a small patch of Jimmy Gibbs! (poor Ellis, Jimmy would understand.)

The Time Bomb (50HP) - A witch variant with an explosive touch. Upon damage or disturbance, she explodes in a blaze of glory. Don't be messing with that witch now.

The Crippler (350HP) - A charger in training. Being tired of only having one big arm, this charger no longer rams, but only punches in hopes of one day being a tank. His punches not only damages survivors greatly, but slows them down temporarily for 30 seconds.

Wetter (??HP) - A boomer that, on top of puking, now leaves behind trails of acid wherever it walks...I guess getting ridden isn't the worst thing the infected can do to you, now is it?

The Extraterrestial (??HP) - A hunter from another realm. This hunter does not follow earth gravity, thus allowing it to jump significantly higher and move significantly faster. Its blood is also pure acid, so upon death, it leaks a pile of goo.