not really new monster idea but kind of goes with more melee (or rather more weapons in general)
various mobs have varying resistances/immunities.
eg: while ordinary post-human Zombies would be easy to maul by everything, more mutated/advanced could be immune to steel weapons (forcing usage of wood board), large stone like creatures would be impossible to defeat using firearms or slashing weapons, while vulnerable to sledgehammers or explosives, security bots that could withstand horrid amounts of damage but could be temporary disabled (and then permanently disabled with electronics skill) with well placed taser shot, or strike with shocker blade, etc.
also new monster idea
Hungry Building
Building size mimic that imitates shop full of loot or food to lure potential prey. Once victim is inside, all means of way outside are suddenly closed off, and interior first turns to light acid (ie:interior turns to ‘acid rain’) to begin dissolving unlucky scavenger. After a while acid levels rises gradually increasing dissolving speed (like whole interior is pool of acid). Once victim dies, Hungry Building rearranges itself and probably change location, to wait for another victim. Some hard items (steel, glass) should resist acid and become part of the building’s loot, and to possibly warn next victim.
(there could be item, room, and mansion sized versions also :D)
