IMPORTANT UPDATE: This article has been updated as of the prerelease of Magic 2014 on July 13; Please refer to the revisions below.

Like many other spells, Rootborn Defenses creates a continuous effect when it resolves: “Creatures you control are indestructible this turn.” If I cast Rootborn Defenses, just going from the wording of the card, it’s pretty apparent that any creatures I control when Rootborn Defenses resolves will be indestructible.

But what about creatures I cast after Rootborn Defenses resolves?

What about if my opponent steals my creature with Zealous Conscripts?

What if I steal a creature from my opponent?

Take a moment and figure out your answer to these questions, and then I’ll walk you through the relevant rules step-by-step.

OK, ready?

The answers to these questions depend on the fact that spells that create continuous effects actually fall into two major categories. The first category — let’s call them Type A spells — includes effects that change the characteristics or controller of an object. The secondary category, Type B spells, encompasses all other effects.

The characteristics of an object include pretty much everything that’s directly printed on the card: name, mana cost, color, color indicator, card types, rules text, abilities, and power/toughness. Everything else that we could possibly know about a card is not technically a characteristic — for instance, being tapped isn’t a characteristic.

If I cast a Type A spell, that spell will “lock in” what its effect applies to when it resolves. This is because a resolving Type A spell determines what cards it can apply to, directly changes those cards’ characteristics (or controllers), and then doesn’t do anything else. For example, if I cast Predatory Rampage in my first main phase, attack with all my guys, and then cast a Centaur Courser, the Courser will be just a 3/3. It won’t feel like much of a predator at all.

On the other hand, Type B spells don’t change characteristics at all. So how do they even manage to affect any cards? Well, they work by literally changing the rules of the game when they resolve. As a consequence, Type B spells don’t lock in the objects they affect.

So, which type is Rootborn Defenses, A or B?

Turns out, it’s Type B! Being “indestructible” is not a characteristic, because it’s not an ability. Rules text such as “Avacyn, Angel of Hope is indestructible” is an ability… but actually being indestructible isn’t an ability or a characteristic. It’s just a statement of something that’s true about a permanent, like saying that my Forest can’t block.

Putting this all together: When Rootborn Defenses resolves, it sets up a game rule that says “Creatures I control are indestructible this turn.” This new game rule constantly adjusts the set of creatures it applies to. As a result, the answers to our questions are:

Creatures that enter the battlefield under my control after Rootborn Defenses resolves will be indestructible.

If my opponent steals my creature, it will not be indestructible while they control it.

If I steal a creature, it will become indestructible as long as I control it this turn.

Today’s Rules Tip written by Paul Baranay, L2 from New Haven, CT

Whoops, time for a re-write! All of this was 100% true back in December, when Paul wrote the tip. However, with the changes to the rules that Magic 2014 has brought us, the Rules Tip Blog staff has gone back in time (so to speak) to correct old articles that will no longer be correct, so nobody accidentally gets incorrect info from us by searching the archives.

As of the release of M14, Indestructible is very much an ability, just like any other. So, going with what Paul was talking about, it has gone from what he calls a ‘type B’ thing to a ‘type A’ thing! As such, Rootborn Defenses will ONLY grant the ability “Indestructible” to creatures that you control as it resolves. Steal a creature later that turn? Not indestructible. Cast a creature spell after Defenses resolves? Not indestructible. Your opponent steals one of YOUR dudes that got the buff? That one -is- indestructible still, where before it wouldn’t be!

Today’s Rules Tip has been updated by Trevor Nunez