Thought Erasure is pretty good bang for your buck. For a blue and a black, you get to peek at your opponent’s hand and have them discard a nonland card of your choice, and surveil 1 to boot- but sometimes, not all of that is going to be possible. Sometimes your opponent doesn’t have many thoughts going on to erase- for example, if they only have lands in their hand, or if they have no cards in their hand at all (if they cast the only card in their hand in response to Thought Erasure, or if you cast it while they were empty handed for some reason). Choosing a nonland card from their hand, in such a case, is an impossible action, and that means that it’s skipped over. It’s just like throwing a counterspell at a Carnage Tyrant, from Izzet Week! Also like Ionizing a Carnage Tyrant, it does not stop the rest of the card functioning; you’ll still get to surveil. So that’s all well and good!
Enter Nullhide Ferox. Nullhide Ferox is an unreasonably large creature with a troubling line of text on it: “If a spell or ability an opponent controls causes you to discard Nullhide Ferox, put it onto the battlefield instead of putting it into your graveyard.”
Let’s go back to the previous situation- an opponent with all land in their hand, but let’s also put a Nullhide Ferox into their hand with it. Here you’ll be hit with a snag- it’s no longer an impossible action to choose a nonland card in their hand. There’s a Ferox right there. Because it’s not impossible, the action isn’t skipped over, and because it’s not optional, you have to pick the Ferox. It gets discarded, and… then you have a problem. Be careful whose thoughts you try to erase!
Today’s Rules Tip was written by Alistair Crook