We can use this same rule to figure out how big other creatures will be when scavenging them. Jace’s Phantasm, for example, can be a Dragon-sized 5/5 when it’s on the battlefield, but in the graveyard it’ll always be a paltry 1/1. The ability that gives it +4/+4 won’t apply, regardless of how many cards are in your opponent’s graveyard.
That’s not the case for creatures with variable power and toughness, though, such as Boneyard Wurm. The */* in its lower right corner indicates that Boneyard Wurm’s ability is a characteristic-defining ability — a special kind of ability that works no matter what zone it’s in. For example, if you have a Boneyard Wurm and two other creature cards in the graveyard, Boneyard Wurm is 3/3. And if you use Varolz’s added ability to scavenge it, it’ll put three +1/+1 counters onto Varolz or whatever you targeted (which was its power at the time it left the graveyard, so it does count itself; it also doesn’t matter what happens to the other two creature cards in the graveyard before the ability resolves).
Today’s Rules Tip written by Jen Wong