zombie mode=mutant mode they are the same thing.
Zombie description
Main zombes are red, there bigger and fatter then normal. The main zombies have these claw things on there back. they got 5,000 HP so beware. 

Secondary Zombies- Same thing except they have tube things on there back and they got 2,000 HP.

They give you 20 seconds to prepare for the infection so make use. There are 2 ways you can use your 20 seconds wisely.

1. Wait it out.. This may seem stupid but its really smart. Ususally people will bunch up in groups too early and if one of them are infected they infect the whole group. So hide away from people and wait to see who gets infected and who doesnt, so you know who to group up with.

2. Glitch, yes 20 seconds is plenty of time to boost your fellow teamates up to high spots or just plain glitch into areas. 13 zone is good for boosting since u cna boost up to the high areas and interest is good cuz u can jump on the lamp posts and u'll outlast your teamates and the zombies for a while.

Weapons:
Bringing the wrong weapons to zombie mode is stupid.

best weapon for the situation is M60 ADv with 150/300 Ammo. it only costs 59,000 GP.

dont bring a shotty, weapons taht have low ammo such as the Kriss super v or the uzi

bring the golden m4 because its accurate and it has more ammo than regular m4.

any other weapon is fine really. i reccomend getting an awm and camping on the high spots in 13 zone unless they group up which is a good time to whip out a deagle not anacodna.