The Karnstruct tokens bridge the gap between the early and mid-game, hitting hard enough to ensure there wont be a late game stage
If you have some copies of Metamorphic Alteration in your bulk, they are worth digging out for sure, but I'd look to sell them now while hype is high, because who knows how strong the combo actually ends up being long term
The floodgate ability is probably for the best though, since Spawn is a sizable threat on board and turns into up to ten mana's worth of spells on the way out
Now, you dont quite win the game on the spot, but if youre able to navigate a game into a position where you are able to protect your Karn and resolve Mycosynth Lattice, your opponent will be completely stripped of their ability to cast anything else, thanks to the one-two punch of Lattice turning all opposing lands in artifacts that now cannot be activated thanks to Karn
Containing Mystery Booster 2, and much much more, this product has been the subject of much speculation this week
The name perfectly encapsulates the effect - it counters any target spell, period