by louper
Regarding the first question, the card says, "If either you or your killer win, ... then you both win." If you get to 20 points, you win. Therefore, you both win.Suppose Player A has the card and Player B kills Player A. Player A returns to the game. Now Player C steals Monster Sidekick. Suppose Player D kills Player C. Player C returns to the game.
Now, basically, Players A and B will win or lose "as a group" and Players C and D will also win or lose "as a group."
If Player B kills both players that have Monster Sidekick, then Player B will win or lose if Player A wins or loses. Also, Player B will win or lose if Player A wins or loses.
Therefore, if Player A wins, for example, Player B wins and therefore Player C wins as well.
Or just house rule it.