Battle negociations and some stuff about levels

[Clipper]

You also asked if you could make an offer to help them on their next combat. You are able to make such a deal if both parties are willing. However, keep in mind that circumstances might change (they might be going for the win, for example), and no such contract is binding. Having said that, you should probably make all attempts to honour the contract if you can, if only to be nice.

But yeah, you can't trade nor forfeit levels as there is no mechanism mentioned in the rules to do so. Giving a helper Treasure cards from the combat, giving any player Items you have in play, or playing GUALs on another player are mentioned in the rules as acceptable things you can do, so you can use them as part of deals for help.