People often share their extra prerelease codes on Reddit, so be sure to have a look there when it's the right time
While that's not the most terrible idea, the likelihood in a Niv-Mizzet deck is that the other spell you're casting is a burn spell that could do the same, and I have to feel that you're going to be better off casting it by itself, rather than putting all your eggs in one basket
(You may cast it from your graveyard for its escape cost this turn.) If a spell you're casting with escape has an additional cost of discarding cards or sacrificing permanents, you may exile cards discarded or sacrificed this way to pay that part of its escape cost
While these tokens arent very big, and you wont get a lot of them without support, its still a nice bonus
EAT BRAINS.
But if you sacrificed to Phyrexian Altar make a mana, then you cannot copy it, since that's a mana ability