I've been having a idea for a new infected.
Think a 4 legged infected who's main purpose is to get a survivor out of a corner/closet/bathroom with a small area of Effect. Here's how he would work:
Mouse 1: Charge (Can't move while doing this)
Mouse 2: Suicide (Area of effect smoke)
The special can not attack, only charge, and he must be at a minimum range to attack a target, the charge would take around 1.5 second to "cast", and the suicide 2 seconds. The survivor who get directly hit by a charge is completely stunned and can not move/attack for 3 seconds, once the survivor hit, the infected will manually suicide resulting a small smoke area dealing important damage if you stay in. The smoke would last around 5-6 seconds and be distinctive from the smoker's smoke.
The infected would be invulnerable to melee, you have to shot him, his carapace would make anything non-shotgun more useful. And his charge cast could be canceled by a melee, pretty much the only thing melee would have on him.
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So far we have 2 infected who pin down Survivors, and one who's got a unique purpose, all these 3 infected can't really deal more than one infected in a corner/closet/small room simply spamming the melee key. I seriously consider a new infected like above would make gameplay even more interesting.
Think about it, the Boomer is very effective in a open hallway with zombies coming from everywhere, the new 4-legged infected would be almost useless in a place like this, unless he use a charge properly. While the boomer is nearly useless against survivors camping a decent spot. Vise-Versa.
In other words, the 4-legged infected + Boomer combo would be deadly if used the way it should be used.