Explosive Collars
The Maniac has the ability to link his victims's lives by tampering with their collars. When the game starts, the Maniac will link his victims in pairs (ofhis/her choice), and if one person in a linked pair dies, the other will die as well (unless healed by Doctor at night or is a Survivor who used protection). Because there are 13 players, at least one player will not be linked with anyone else at start (making him vulnerable to Witch). Because Witch can roleblock linked players and kill unlinked ones, roles like Sheriff and Doctor needs to be very careful and not reveal their linked partner to the Witch, least they get roleblocked. The Maniac cannot be roleblocked, but he can be still accidentally killed by Witch if he chooses not to link himself with anyone. Generally, the Maniac will probably try to link himself with another player, but even that strategy is not without any risks, because Maniac can still die if his linked target gets lynched (even if he is a Victim).
Also make sure that your linked partner is not a Sadist! This will apply to both Victims and their enemies, particularily Survivors. The only person who can change the collar frequencies is the Maniac, but you will probably need to force a lynch in order to make him to do that action again.
The Maniac can leave more than one player unlinked (three or five), giving the Witch a better choice of targets. However, the victims can try to make "false" links to fool the Witch. Maniac himself can link together any number of pairs in a simple night.