In the rules it says you can interfere with combat "use a one shot item to help another player by casting a potion against his foe"
My friend drew a lvl18 card and someone else helped him. I wanted to play a flaming poison potion to add +3 to their side and "help" them. Then by the wording of the rules, as an elf, do I go up a level?
According to the Munchkin FAQ under Important Note #2: Playing/Using/Switching Items During Combat:
Playing/using a one-shot Item during a combat that aids the munchkins (and not the monsters) does not constitute "helping" in combat, as described in the rules. This means that in any given combat, any number of players can play cards to aid or hinder either side as often as they want, as long as they have the cards. Only one other player can actually join the combat as a helper, however.
So, no, this would not actually constitute "helping" in the combat to satisfy the Elf racial ability.
However, if through some other means you had actually been the helper in the combat, then yes you could have won or tied, as long as the card that allowed you to help did not specify that the level gained could not be the winning level, because according to the FAQ under Important Note #1: Reaching Level 10:
Note also that ANY level gained as a result of killing a monster counts as the winning level.
And also from this post on the official Munchkin forum
The level the Elf gains for helping in combat can be the winning level, because it's a level gained as the result of winning a fight.
The answer's very likely that no, that doesn't count.
It isn't the kind of help talked about in the Asking for help section, where you actually join the combat and are at genuine risk of suffering Bad Things if you lose. Vitally people can refuse help offered this way, and limit the elf's ability to gain bonus levels.
Interfering with combat by playing cards to benefit the player involved is, however, called "help". But there's lots of other risk-free things you can do to "help", including telling the player to use their own consumables, or getting them a glass of water to help them think and focus on combat.
Ultimately if this comes up it probably should be resolved by a loud argument with the owner of the game having the final word. I would probably argue against it, since elves will have an unstoppable, risk-free ability to gain quite a lot of levels.
(To your title of whether you can help and win the game: you can't reach level 10 by helping this way as an elf, as you didn't kill a monster yourself, you just helped someone else who killed one.)
If you use a "Dark" race modifier then causing your opponent to lose could win you the game if there loss causes their character to die.Otherwise, no an elf interfering one way or the other would not yield a win unless they were actually in the combat.
https://s-media-cache-ak0.pinimg.com/originals/68/10/40/6810402a1635377095ac830016f9ebfc.jpg
Sure, if you own the game, since the rules state the owner of the game resolves disputes, and otherwise change the rules as they see fit; it won't be fun for the other players, however.
