The active player, in this case, likely the player controlling Hulk, chooses the order, so you can choose to move and Quake again before you can no longer Quake.

Add written, as long as you hit someone, you would be able to continue activating it. However, I would expect this to get Errataed with "Once per character...", and would expect any judge to reasonably limit it so.

I'm not sure why you'd expect this to happen, and no, judges should absolutely not be making rulings that are wholly unsupported by the rules.

It's a specific interaction that requires exact positioning to happen at all. It's easily avoidable for the opponent. There are far more ridiculous things that require far less effort, like just playing prime Vulture by himself. WK's has already weighed in on that. The chance of Korath getting errata'd because of this interaction is basically zero.

I'm not sure how this requires 'exact' positioning, or how it would be really avoidable. Go wherever you would like, then your opponent runs Korath up to you, the Hulk runs up to you. Even better, use Wasp to make Hulk colossal, have Hulk carry Korath, then Quake with Giant Reach 3. And, unlike Vulture who needs to KO, all Hulk needs to do is get a successful hit, which means even a successful Impervious would allow him to continue attacking, with an early attainable 15 attack, no need to worry about damage because you can just keep attacking. This far outweighs what Vulture can do. I am usually very strict on playing by the rules as written, but I find this to qualify as an 'exploit' or 'loophole' that undermines tournament integrity, but this of course just my opinion. Others may not care how their players feel about having that one player roll 20+ attacks in round 2, winning every match before their opponent even finishes setting up their opening move.

It requires exact positioning because Hulk needs to remain adjacent to Korath the whole time. Adding in a way let Hulk carry Korath makes it more of a challenge, but it's still not difficult to play around. It might be decent, but there's nothing even close to an exploit or a loophole here. It folds to good positioning and damage reducers.

It might fold to Super Senses and Shape Change, but it doesn't fold at all to 'any' damage reducers, as it doesn't require KO'ing, or even damaging, but only hitting. The only positioning 'I' see avoiding this is wrapping your team in Barriers on an indoor map every single round, but I am kind of tired right now, so maybe I'm being short-sighted. Either way, I'll agree to disagree!

It's not actually that difficult to position two characters with Invuln (or better) so that Hulk can't get a single target Quake off, especially if you choose the map. Hulk getting Giant Reach makes it even easier. And yeah, that's not even taking things like SS or SC into account.

This is one of those things that sounds insane on paper until you see it in action against a clever player.

I could *maybe* see an intent ruling that nested actions still count for their parent action having attacked, i.e. Charge/Running Shot.

Even that seems highly unlikely unless that has been the rules intent all along and we never knew about it before. Can't come up with any older effects where this distinction would matter.

My team mate ran this at nationals and was undefeated in 5 rounds of swiss, despite never winning map. He was the 2 seed going into the cut. However I feel that his build gets no love because it isn't Kobik, Thanos or Vulture.

Turn 1 retrieve Canister and destroy next to Hulk, put Gas marker on Hulk, Barrier up with Rusty.
Turn 2 roll for Canister and hope you don't loose it. Double hug (perplex attack) Hulk with Big Tonys, make Hulk colossal with Wasp by spending plot points. TK out Hulk 6 squares place another 2. Move Korath next to Hulk, place Pym Pocket Tank adjacent to Korath and Hulk. Sidestep Wasp next to Mister Oz carry Mister Oz with Wasp closer to the opponent furthest away from Hulk. Leap/Climb Hulk 10 squares (Avengers TA) carrying Korath, place Pym Pocket Tank adjacent to Hulk. Quake at no cost with the option to throw the tank to reposition opposing figures (-1 attack). 21 to 19 square swing, 15 attack, 5 damage, Giant Reach of 3 with Battle Fury.
Sidenote: at Nationals a judge (not sure who it was or the explanation) ruled that Hulk couldn't resolve all mystics damage after all no cost Quakes were resolved. I believe this is contradictory to the rules.

Force Build 9149469 0
Set	#	Name	Team	Pts	Value
CMM	019	Korath		75	SELL
TMT	106E	Hulk		50	SELL
AI	G011R	Wasp, Heart of the Avengers		50	SELL
RE	052E	Mister Oz		40	SELL
EAX	030	The Skull		40	SELL
HQ	004	Big Tony		15	SELL
HQ	004	Big Tony		15	SELL
WKM	MP17-007	Pym Pocket Tank		8	SELL
JW	S100	The Joker's Gas Canister		3	SELL
XXS	XID-004	Rusty		3	SELL
Force Total:				299	$0.00

The Joker's Gas Canister has since retired, so, this build is not legal for Worlds.

Giant reach is optional, so it actually just makes Hulk much better. He can choose to only target adjacent figs until he has beaten the brick to death, then he can do giant reach 3 to reach far and be sure he hits somebody as he moves one square at a time closer to his other targets.

But I do agree with your overall point that it would be wrong for a judge not to permit this and that it isn't clearly the most dangerous combo in the game. Just another clever powerful team to have to learn to deal with.

That is definitely wrong. Korath lets you move "after resolutions," Hulk gets a quake at no cost "after resolutions," and Mystics damage happens "after resolutions." Active player can put the mystics damage off until the very end.