Half-Life

Gee Urosevic says:

Poison Zombies can take a lot more damage than other zombies (roughly 300%), and have better attack capabilities. Thankfully, they are rarely encountered.

The best tactic when facing a Poison Zombie at close range is to move around while attacking to avoid being hit by the thrown headcrab. Normally there are 3 riding headcrabs. When a thrown Poison Headcrab comes into contact, health points will drop to 1 but will gradually increase by increments of 10 as the HEV Suit administers an antidote to the poison. Therefore, it is advised not to use the crowbar against incoming thrown headcrabs. It is best to gain some distance to avoid the reach of the headcrab.

The most effective weapon against Poison Zombies is fire: when hit, the zombie will set alight the headcrabs as well when dying. A very good tactic is to grab a propane tank or gas canister, pop out of cover, light up the zombie then take cover before it throws headcrabs. It will die and take its passengers with it without causing any damage. If no flammable objects are present, take advantage of headcrabs and their host’s flammable nature by chucking hand grenades or firing MP7 grenades.

If none of the methods above can be practiced, another tactic, when the player has energy cores to spare, is to equip the Pulse Rifle and use its alt-fire on the Zombie. It will disintegrate the zombie with all passengers because as soon as it dies, all headcrabs will detach; however, they instantly touch the fusion orb as well, which means immediate death.

Because Poison Zombies tend to move quite slowly and are a big target, it shouldn’t be hard to hit them. Emptying a magazine into a Poison Zombie from an SMG1 or any other firearm will generally kill it. Explosives, such as SMG1 grenades and regular grenades, also work well but using the rocket launcher is a little wasteful, as there are better things it can be used for unless there is a rocket ammo crate nearby. It is, however, quite satisfying. The Shotgun, though, is a good way to kill individual Poison Headcrabs. Also, they can easily be killed with one hit from the crowbar because of their delay in jumping at you. A longer-ranged weapon may be advisable, though, because one does not want to get too close to this zombie.

In the Ravenholm chapter there are three Poison Zombies that carry three or more headcrabs each, but there are plenty of explosive barrels and gasoline containers that come in handy.

If there is no available AR2 secondary fire, SMG secondary fire, grenades, or flammables to kill the zombie with, another tactic is to wait until all its headcrabs are thrown off and killed. The zombie should be a minimal threat without the hitch-hiking poison headcrabs on its back.