If my opponent plays a card that would destroy Welding Jar, can I respond by sacrificing it and putting a regeneration shield on another artifact I control? Or can Welding Jar's regeneration ability only be used on an artifact that is about to be destroyed?
If my opponent plays a card that would destroy Welding Jar, can I respond by sacrificing it and putting a regeneration shield on another artifact I control?
Sure.
Or can Welding Jar's regeneration ability only be used on an artifact that is about to be destroyed?
The rules don't have a concept of "about to be destroyed". You can use Regenerate effects on any valid permanent, regardless of having or not a reason to believe it will be destroyed this turn.
That's what I thought. The reason I asked is because I thought I saw a card recently that made the distinction where a certain ability depended on a creature having regenerated in response to being destroyed although I don't remember any other details. The Gatherer ruling for the card I am thinking of said something along the lines that you couldn't trigger the ability simply by activating a regeneration shield. Or was the restriction that you weren't allowed to regenerate your opponent's creature. I'll see if I can find the card I am referring to.
That's what I thought. The reason I asked is because I thought I saw a card recently that made the distinction where a certain ability depended on a creature having regenerated in response to being destroyed although I don't remember any other details. The Gatherer ruling for the card I am thinking of said something along the lines that you couldn't trigger the ability simply by activating a regeneration shield. Or was the restriction that you weren't allowed to regenerate your opponent's creature. I'll see if I can find the card I am referring to.
You may be referring to Spiny Starfish's triggered ability. This ability cares about whether and how often Spiny Starfish regenerated this turn, not necessarily whether or how often a regeneration effect that applied to Spiny Starfish was created. However, this is not clear from the rules, which speak of what "regenerate [permanent]" means (C.R. 701.14a-b, 614.8), or say that "[n]either activating an ability that creates a regeneration shield nor casting a spell that [does so] is the same as regenerating a permanent" (C.R. 701.14c), but not necessarily that the "creation of a regeneration shield" is or is not the same as the event of a permanent "regenerating", that is, the event that replaces a permanent being destroyed due to regeneration. That is a gap that the rulings you speak of fill.
Or was the restriction that you weren't allowed to regenerate your opponent's creature.
You are totally allowed to regenerate an opponent's creature.
Some confusion often arises because a creature that regenerates gets tapped; some players thought that they could tap an opponent's creature by casting some regenerate effect on it. That doesn't work.
The creature taps only if it actually regenerates, when damage or some other effect actually ties to destroy it. Simply being the recipient of a regenerate effect does not tap it. (rule 701.14c)
Found the card I was thinking of, it's Debt of Loyalty. The distinction made with this card was applying the regeneration shield vs "using up" the regeneration shield. In order to successfully take control of the targeted creature with Debt of Loyalty, the targeted creature has to actually "use up" the regeneration shield (i.e. be destroyed).
Sure.
The rules don't have a concept of "about to be destroyed". You can use Regenerate effects on any valid permanent, regardless of having or not a reason to believe it will be destroyed this turn.
That is a gap that the rulings you speak of fill.EDIT: Edited after comment 6 was posted.
Some confusion often arises because a creature that regenerates gets tapped; some players thought that they could tap an opponent's creature by casting some regenerate effect on it. That doesn't work.
The creature taps only if it actually regenerates, when damage or some other effect actually ties to destroy it. Simply being the recipient of a regenerate effect does not tap it. (rule 701.14c)
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)