If you cannot win a combat on your own, you may ask any other player to help you. If they refuse, you may ask another player, and so on, until they all turn you down or someone helps. Only one player can help you, adding their combat strength to yours.
Anyone can play cards to affect your combat, however!
You’ll probably have to bribe someone to help. You may offer your helper any Item(s) you are currently carrying, or any number of the Treasure cards the monster has. If you offer part of the monster’s Treasure, you must agree whether they pick first, or you pick first, or whatever. You may also offer to play any cards from your hand that you legally could, such as Go Up a Level cards, on your helper. The special abilities or vulnerabilities of the monster also apply to your helper, and vice versa.
A few cards or abilities allow you to compel another player to help you in combat. These abilities do not work if you are fighting for the win – and if you force someone to help and then the fight becomes one for the win, your helper gets to back out without penalty. However, if you voluntarily help someone, you don’t get to back out just because they’re about to win the game – so pay attention!