Just got this guy. Goblin king can use Chosen powers "until next turn". When does that end? Can he roll for leadership if he chooses it?

Pg. 10 in the rulebook, under "Clear Phase"-
Goblin King won't ever be able to use Leadership during your Beginning of Turn phase via his trait. He wouldn't get either effect from it, since they are BoT triggers.

Effects that lasts until your next turn ends at the end of the clear phase of your opponent's turn.

Rulebook page 10:

Thanks. I had A feeling that was the case.

It's not entirely useless, though. You can at least get the +1 action for it, since that's a static thing now. It would be a severe corner case where that might be more helpful than another option, but that much can work.

The +1 action total also comes at the beginning of the turn, so you don't get that either.

Yes, it is entirely useless. This is exactly why I quoted Leadership and gave an explanation as to why that doesn't work.

Not entirely useless. You could choose him for Inspiring Command:

and your opponent could have Leech:

and say that you can't choose to use Mastermind.

Except he has Power Cosmic. So, still useless.

Sad, but true.

Unless Scarlet Switch, Nick Fury, etc, prevents the use of Power Cosmic on those lower point characters...

Or unless you win the lottery and are able to buy NECA and thus own Wizkids and make Feats modern legal again and change Goblin King's wording!

I mean, yes, I get that there is a scenario that can be manufactured where such an unlikely confluence of events would fit an unlikely build.

But that's not what anyone is talking about.

Least of all in the Rules forum.