These two come to mind as X spells that aren't unreasonable without the doubles but are absolutely nutso with them. Of course, this depends on how hard you want to push mono-B, as the direct damage mode on the command can get a little out of hand. This might be within your tolerance/an acceptable reward for leaning into the B devotion deck, though.
The card not rendering is the new Vorpal Sword from AFR. These are all reasonable without the doubling and pretty sweet with.
There's also this card, which I never knew existed until now. I'm not recommending it, mind you, but...look at it.
Isn't it just wild?
Edit: screw it, I'm officially recommending Helldozer. I've never played with it, but damn, it just looks like so much fun. This is what land destruction should look like.