Is there a way to do some mob team events? For example, i have a block that spawns 4 zombies when a player is near it. I want to spawn a chest when all the 4 zombies are dead, how can i do this?

keep track of the entities, every tick check if the entites are dead, if they are spawn the chest.

 

Hard part is the keeping track. You could easily check if ur entites die, using LivingDeathEvent, problem is keeping track of despawns I guess..

Could you please send me a link to a LivingDeathEvent example? For the despawn i can think a workaround: if the player dies in the fight despawn all the zombies (so the reward is spawned only if the player wins)

http://www.minecraftforum.net/forums/mapping-and-modding/mapping-and-modding-tutorials/1571567-forge-1-6-4-1-8-eventhandler-and

using google isnt that hard

What I would do is create a bounding box within which I would check which entities are tracking the player. Then check if these entities have died or not. Look at

 @SubscribeEvent(priority=EventPriority.NORMAL)
public void onTracking(PlayerEvent.StartTracking event) {}