The mimic kill token is an item that allows the player to fight the Giant Mimic. They can be obtained while killing monsters or skilling, or from a Giant Mimic loot crate. When a token is received by skilling, the following message will be shown:
Congratulations, you have obtained a Mimic Kill Token while skilling! It has been added to your backpack.
Mimic kill tokens are a universal drop, which means they are able to be obtained from any monster or skilling activity in the game.