Mutation also plays VERY well with +1/+1 counters, like the ones from Evolve. It makes the ‘base’ creature into an X/X. So say you have a Cloudfin Raptor that’s been evolving a few times this game, and it currently has 3 +1/+1 counters on it. After you resolve that Mutation for X=5, it’ll be an 8/8 flier, because of the 3 counters. You can also use it to force an evolve if you really need to, by making your creatures SMALLER. You can cast it for X=1 to make your Adaptive Snapjaw into a 1/1, so your 2/1 Shambleshark will evolve it. Likewise, you can cast it for X=0 to kill your own counter-less creatures if you need to, by making them into 0/0. Kinda like the old Mirror Entity trick!
Finally, we’ll cover how it interacts with other ways of messing with power/toughness, besides counters. Say you cast a Mutation for X=4, and then your opponent hits one of your guys with Snakeform. Your guy won’t be a 4/4, it’ll be a 1/1. But if you do that the other way around, your Snake will be a 4/4; that’s because both of these abilities are trying to set the P/T to a specific number, and whichever one is newest ‘wins’. And like counters, any static boosts/debuffs [like a Gaea’s Anthem or your opponent’s Elesh Norn, Grand Cenobyte] will apply AFTER Mutation. Lastly, things that have characteristic-defining abilities [think Consuming Abberation or Rubblehulk] will get ‘overwritten’ by Biomass Mutation. You have 10 lands, and cast Mutation for 8? Your Rubblehulk is now an 8/8, not a 10/10. Oh, and Mutation only works on the creatures that were on board when it resolves; if you cast that Mutation for 6, then cast a Shambleshark, the Shark will only be a 2/1, not a 6/6.
Today’s Rules Tip written by Trevor Nunez