Meaning of "by yourself" on High card

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Originally Posted by UncleBob

So, let's say I'm at a combat strength of 12 and the monster is a level 15. Player B offers to play a +5 card on me if I give him one of the two treasures. I agree.

This is illegal. There is no method by which you are allowed to give him Treasure cards earned via the battle. Player B can make an offer that requires you to give him an Item after the battle (via trade of Items on the table), but he can't take the cards directly.

The High card says that you have to give up all the treasures "you get" - do you actually ever "get" the treasure you're giving up?

No. Read it as exchanging all the Treasures you are entitled to. They are never actually drawn if you do decide to exchange them.