Willbreaker

[Kaylesh]

That's not in the CR indeed, for tournaments there is a code of conduct in the tournament regulations though
But I get what you're saying. I too have seen cases where things should work (according to my logic) yet don't.
Don't overestimate the power of this combo though. It requires quite a boatload of mana & WB to sea on the field, under your control, otherwise your stolen creatures return to its former controller. (Unless you overwrite with {goblin auctioneer} eg). And there's things like {homeward path}.

[griffin131]

The ability goes on the stack, but unless you pay you can't TARGET. Which is required for willbreaker

The ability cannot go on the stack until all instances of "target" are satisfied.

[Double-O-Scotch]

How can all instances of target be satisfied if you opt not to pay the 8. Seriously, wtf people?

[griffin131]

How can all instances of target be satisfied if you opt not to pay the 8. Seriously, wtf people?

Because it goes in the stack before you pay 8, and it has to have targets before it goes on the stack.
Seriously, that's how the rules work.

[griffin131]

114.1d: A triggered ability is targeted if it identifies something it will affect by using the phrase "target [something]," where the "something" is a phrase that describes an object, player, or zone. The target(s) are chosen as the ability is put on the stack; see rule 603.3d.

[griffin131]

117.12.: Some spells, activated abilities, and triggered abilities read, "[Do something]. If [a player] [does or doesn't], [effect]." or "[A player] may [do something]. If [that player] [does or doesn't], [effect]." The action [do something] is a cost, paid when the spell or ability resolves. The "If [a player] [does or doesn't]" clause checks whether the player chose to pay an optional cost or started to pay a mandatory cost, regardless of what events actually occurred.
Example: You control Standstill, an enchantment that says "When a player casts a spell, sacrifice Standstill. If you do, each of that player's opponents draws three cards." A spell is cast, causing Standstill's ability to trigger. Then an ability is activated that exiles Standstill. When Standstill's ability resolves, you're unable to pay the "sacrifice Standstill" cost. No player will draw cards.
Example: Your opponent has cast Gather Specimens, a spell that says "If a creature would enter the battlefield under an opponent's control this turn, it enters the battlefield under your control instead." You control a face-down Dermoplasm, a creature with morph that says "When Dermoplasm is turned face up, you may put a creature card with morph from your hand onto the battlefield face up. If you do, return Dermoplasm to its owner's hand." You turn Dermoplasm face up, and you choose to put a creature card with morph from your hand onto the battlefield. Due to Gather Specimens, it enters the battlefield under your opponent's control instead of yours. However, since you chose to pay the cost, Dermoplasm is still returned to its owner's hand.

[griffin131]

So, due to 117.12, we know that the cost is paid during resolution. Due to 114.1d we know that targeting is done as it goes on the stack.

Targets are chosen prior to the optional {8} cost.

[Kaylesh]

Courtesy of Kaleo

"Whenever a trigger says "may", you don't decide if youre doing it or not till resolution. However if it says "target" you have to choose a target when you first put the ability on the stack. So choose a target and then when resolution comes around you choose not to do the thing but you already gained control of the thing since you did target it."

That's the way. Compliments on the wording.
It could even be an ability says "... Target creature an opponent controls". In that case, the ability would be countered, yet you still get to keep the creature.