I've definitely been the guy that gets 4-5 cards deep into an opponent's series of spells that wins them the game while totally forgetting that I had a counterspell in hand. And I was just playing one deck at the time! So I think it's fine. Plus that was a super cool way to end the game. It was super impressive to burn through two life totals above 50. And you were right about Lightning Axe. Mizzix Mastery lets you cast the spells without paying their mana costs so you'd need to pay any additional costs if you want to cast a spell that has one.
I've definitely been the guy that gets 4-5 cards deep into an opponent's series of spells that wins them the game while totally forgetting that I had a counterspell in hand. And I was just playing one deck at the time! So I think it's fine. Plus that was a super cool way to end the game. It was super impressive to burn through two life totals above 50.
And you were right about Lightning Axe. Mizzix Mastery lets you cast the spells without paying their mana costs so you'd need to pay any additional costs if you want to cast a spell that has one.