I assume you mean creatures with level up like Knight of Cliffhaven rather than Leveler? :) In which case, is this the same as Level-Up Cards?

Yes, and that update never brought levelers :

That's true. It turned out to be somewhat tricky (you basically need three card text boxes and three sets of P/T, which my infrastructure isn't set up for).

I'd probably rather you commented on that feature request (which is still open, blue) rather than create a new one. But nevertheless, okay, request heard. It is somewhat tricky so I don't know when I'll be able to do it, but I'll give it another look.