Put a +1/+1 counter on each creature you control
The cheaper a given effect is, the better and stronger it can perform, and this is the perfect example of that
Recurring Nightmare works for that too
Prince Johns Got You Covered
Her second ability is even more annoying, shutting down a lot of random cards that let you cast spells "without paying their mana cost." From my own decks, Rishkar's Expertise gets a lot worse in my Xenagos, God of Revels deck, my favorite card in Tribal Zombies, Rooftop Storm, gets neutered as well, and Animar, Soul of Elements can't cast Ulamog, the Infinite Gyre for free
I simply instruct them to pay their creature's Morph costs, and then belt out an evil laugh when they understand the implication: they can't turn their creatures face up