Rule Of 4

Opponents are only able to control up to 4
Hunter creatures
You may select 4 Hunter creatures you control,
those Hunters gain the abilities of all other
Hunters on the battlefield and in your library
In order to stop the deaths of more hunters, the
Hunter's Guild added a rule that only allows four
hunters to hunt together. Despite this rule by the
Hunter's Guild there are a few exceptions to this rule, however.