Opportunist is a passive skill in the Wind Master skill tree which causes your shaman automatically enter the hole once the last mouse alive enters the hole.
This is useful for shamans who either want to increase the "Cheese personally gathered" stat, or who simply do not wish to have the round drag on if they can't get to the hole in time. You do not need to have the cheese for this skill to be triggered.
If the last mouse dies in any way, this skill will not be triggered.
However, the skill will trigger upon the use of Easy Victory on the last mouse.
In Dual Shaman maps, if both shamans are still alive after the "last" mouse goes in, the skill won't activate until one of the last two shamans goes in the hole.