If there is a will, there is a way... If you use my Special Resource Pack (SRP) idea, You can shape a block like a monkey... After that make the zombies wear leather armor and that Monkey Shape block. (Maybe you can paint the leather armor too" Or easy way, give zombies speed. and change their textures with SRP. And you said fog, you mean flames??? I think you can make a scoreboard-thing that recieves points when you walk in cobweb. When you got that points, you gain poison or damage. Hard part is making cobwebs move. But I think It's easy with plugins, right? And water heal; That scoreboard loses points while you are in water. If you don't wanna mess, you just can make a plugin for that... And bloodrain... Blue blood, seriously? Im sayin SRP again...
Edit: OMG find an awesome way! I played in a famous server, there were a rule that says Server textures must be on. Why dont you do same? You can make a special server texture. Sooo, when you join qq, your resource pack will automatically change and here is awesome realistic Catching Fire map.!