Q: My friend and I somehow always seem to have the same argument almost every other day: what exactly does "indestructible" mean in Magic? We both agree that it cannot be destroyed by most spells, but it can be removed from the game or put on top on the owners library etc. The only thing we can never agree on is whether or not the creature would be killed if it has a toughness of 0.
A: From the Magic Rules Corner:
The release of Shadowmoor brings us Shield of the Oversoul—the first common card that can make a creature indestructible—and that's raising questions of what exactly being indestructible means.
Let's start by looking at what exactly "destroy" means. When a permanent is destroyed, it's put into its owner's graveyard, but that doesn't mean that every permanent that's put into a graveyard is destroyed. In fact, there are exactly two ways for a permanent to be destroyed:
- It can be destroyed by a spell or ability that specifically uses the word "destroy" (like Terror does).
- It can be destroyed by the rules of the game if it's a creature and it's been dealt lethal damage (damage greater than or equal to its toughness).
A permanent can go to the graveyard or be removed from play otherwise in many ways, but only these two are "destroying" it. That means that being indestructible—much like regenerating—can stop either of those two things from happening, but it can't help against anything else.
With that in mind, let's look at the glossary definition of "indestructible" from the Comprehensive Rules:
If a permanent is indestructible, rules and effects can't destroy it. Such permanents are not destroyed by lethal damage, and they ignore the lethal-damage state-based effect (see rule 420.5c). Rules or effects may cause an indestructible permanent to be sacrificed, put into a graveyard, or removed from the game.
The "rules" part of "rules and effects" refers to the rule that says that a creature with lethal damage on it is destroyed. (In Magic, damage doesn't kill creatures; state-based effects do.) The "effects" part refers to more straightforward cases such as Terror that actually say "destroy." In other words, as you pointed out, a creature that's indestructible isn't destroyed for having lethal damage on it, and effects that say "destroy" don't destroy it.
Being indestructible doesn't protect the creature from leaving play in other ways. As you and your friend agree, it can still be removed from the game (say, with Last Breath), returned to its owner's hand (with Unsummon, for example), put on the top or bottom of a library (with Æthertow or Condemn, perhaps), etc. Sacrificing a permanent doesn't destroy it, either, so neither regenerating nor being indestructible can stop a sacrificed permanent from going to the graveyard..
Shadowmoor's -1/-1 counter theme brings your final question to the forefront. Can an indestructible creature be killed if it has a toughness of 0 or less? Think back to the definition of "destroy." Having 0 or less toughness doesn't cause a creature to be destroyed; it causes it to be put into its owner's graveyard as a state-based effect (that's rule 420.5b). The same is true for two or more legendary permanents with the same name, two or more planeswalkers with the same subtype, and Auras that aren't enchanting anything or are enchanting something illegal. Being indestructible won't keep a creature from going to the graveyard for having 0 toughness or for having the same name as another legendary permanent. Note, however, that if an indestructible 2/2 is the target of Puncture Bolt, it won't be put into the graveyard, as it's now a 1/1 with 1 point of damage on it. The fact that its toughness was reduced doesn't matter, only that its toughness is still above 0.
Two other points while we're on the subject:
Being indestructible isn't the same as regenerating. Regenerating a permanent replaces the event of that permanent being destroyed with something else: removing all damage from the permanent, tapping the permanent, and (if it's in combat) removing it from combat. Some creatures, such as Mossbridge Troll, regenerate every time they would be destroyed. This means, first, that anything that would destroy the creature instead has the effects that regeneration normally does; and second, that effects such as Terror's will still destroy it, because Terror says, "It can't be regenerated." Neither of these things is true of an indestructible permanent. It's also worth noting that an indestructible permanent never regenerates, because it's never the case that it "would be destroyed."
Being indestructible doesn't prevent damage, nor does it counter spells. If a creature with lifelink deals 3 damage to an indestructible 3/3 creature, the controller of the creature with lifelink will still gain 3 life (and, unless the creature with lifelink also had wither, the indestructible creature will have 3 damage on it until the end of the turn). If an indestructible green and/or white creature is the target of Gloomlance, it won't be destroyed, but its controller will still have to discard a card. If an indestructible creature takes damage equal to or greater than its toughness, then stops being indestructible later in the same turn (say, because the Shield of the Oversoul enchanting it is destroyed by Gleeful Sabotage), it will be destroyed. The same is not the case if it's destroyed by a "destroy" effect and later stops being indestructible—"destroy" effects only care whether the permanent is indestructible at the particular moment they try to destroy it. Finally, if a source with wither deals damage to an indestructible creature, that many -1/-1 counters will be put on the indestructible creature. If this reduces the creature's toughness to 0 or less, it's put into its owner's graveyard just like any other creature.
Indestructible, yes. Unkillable? Not so much.
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