Ok Question.
If joker masterminds 3 clicks of damage to say Ultron who is standing next to him, does Ultron only take 1 click because of his invulnerability? thus removing 2 clicks?

Thanks.

yes

Except that Joker can't mastermind to Ultron, because Ultron is more expensive than Joker

You can only Mastermind to another figure that has a lesser cost.