You won't have to pay the commander tax to activate that ability, and activating that ability won't increase the commander tax to pay later
Here's the rest of our original critique of the deck: While the Merlin/Madam Mim Bounce package is strong and will surely see play in the new meta, there aren't enough of them in this deck to create a reliable strategy
While others were amassing their forces, getting combos going, and throwing horrifically powerful beasts at each other, I dutifully worked away at the quest list so no one saw my most powerful move coming an onslaught of Blitzballs from a Walking Ballista
The artwork shows Encanto's Mirabelle, Bolt sporting a steampunk-esque leg attachment, Belle from Beauty and the Beast stepping into her father's footsteps with an engineer's outfit and an electric tool, The Mad Hatter brewing some tea, and Iago with his brazen scowl
Then, Madam Mim can bounce him safely back into your hand, setting up a vicious cycle that, if it isn't stopped, can give you a huge lore lead