Elves and one-shot items?

[Vanderbilt]

So my group and I are all new to munchkin (base game) and came to a couple questions tonight while playing.

For a player that is an elf, if they use a one-shot item, like magic missile, to help another player win a combat, does that count as helping to kill a monster so the elf player would gain a level?

The other question is if there is any sort of time frame to use mutilate the bodies.

Example: Player A wins combat and ends their turn. Player B starts their turn. Player C wasn't paying attention and now wants to play mutilate the bodies to gain a level saying that the combat just happened. Other players are saying it is too late and they would have to wait for a new combat.

Thanks for helping^^