Various questions
 

When you are asked to lose an item.

Are we allowed to lose a small item that is not currently equipped and is currently Carried ?

Which leads to the next part of the question. When losing a small item, i understand that it says anything that doesn't state "big" is considered small. But do we follow that literally?

Like, am i allowed to lose a One-Shot card? A card that doesn't say how much it's value is?

Questions about class abilities.

Wizards

Are we allowed to use the wizards skill to cast away the monster which another player is fighting?

Thief

Are we still allowed to steal when we are at level 1? or what happens when we fail to steal the item when we are level 1?

One Shot

Are we allowed to use cards to force the monster to disappear during another player's turn when they are against a monster?

E.g. Player A is at level 9 and about to kill the monster to win the game and Player B uses a card to instantly destroy the monster, lets player facing the monster get the treasure but no level. <<-- Are we allowed to do that?


Thank you

Re: Various questions
 

Nearly all of these questions are answered in the Munchkin FAQ, which I encourage you to bookmark now and peruse as you have time.

It depends on the wording of the card. If it doesn't specify an Item in use, then yes, any Item you have in play is fair game.

Any Item (a card with a listed value in Gold Pieces) that doesn't say "Big" is small. Cards that don't have anything at all shown for value are not Items, and therefore are neither Big nor small.

Only if you are the helper in the fight. Wizards cannot charm monsters they are not fighting at the time.

Yes, a Level 1 Thief can steal. If he fails, he discards a card and that's it.

Unless the card says it can't be played then, sure.