BOVINE wrote: ↑4 years ago
Edit 3 for rules clarification: How do i determine when to use "When you do," vs "If you do,"? Thanks
"When you do" is used if the effect following is has a target that you don't necessarily need chosen as the first part of the ability resolves e. g.
Heart-Piercer Manticore doesn't require you to choose a target before you even sacrifice the creature (with "If you do" you'd have to choose all targets as the ability goes on the stack).
Another situation where "When you do" is used is if your ability in itself is not triggered or activated, but you want part of it to use the stack (to be interactive), so you create a triggered ability within e. g. all kind of exert-on-attack creatures don't necessarily have targets (though some have and for consistency alone using "When you do" on all of them is nice anyway), but all use "When you do".
The rule of thumb with a choice is kinda correct, but extremely incorrect for e. g. a triggered ability where the first half is a nontargeted drawback (and should be mandatory), but the second half is a targeted pay-off:
At the beginning of your upkeep, sacrifice another creature. When you do, target creature an opponent controls gets -3/-3.
Targets after "When you do" are not chosen for the upkeep-triggered ability, so you cannot avoid sacrificing another creature if you control one (generally...) But once you do, you get the second triggered ability and choose targets... if there are any.
Now with "If you do" you might control this and another creature and your opponents control no creatures. The target has to be chosen immediately, but since there is no legal targeted the
whole ability does not go onto the stack and you get around the sacrifice - which is in this case not intended.
But on the other hand
Heart-Piercer Manticore also uses it, despite a may. And
Glorybringer has to use it, since a static ability cannot target.
tl;dr: The three most important things "When you do" does are:
- Delay the choosing of targets
- Enable choosing targets in a static ability
- Create an additional chance to interact with abilities since it forces part of an ability to use the stack (a second time if already part of a triggered/activated ability).
Most important situation
not to use "When you do": If the part you are introducing is done during a complex act that should not be interrupted by passing priority and people playing spells and abilities in reaction e. g. while searching your library, scrying, making piles etc. The "When you do" part will only happen after an opponent had a chance to play spells and the entire rest of the effect (e. g. shuffling for a search) has occurred, so it cannot interact with e. g. you looked at before shuffling.