That's why Upheaval is such a bomb: there are virtually no ways to deal with it, and once it is cast you can end up with two to three creatures plus a land on the board while your opponent literally has nothing, and has a hand full of sixteen cards they need to discard down to seven
Right now I have it in so that I have something good to return with The Mending of Dominaria, but maybe a better plan is to use Bone Dragon and not The Mending of Dominaria, either just relying on Devious Cover-Up or possibly using Bone Dragon to sculpt your graveyard for Gaeas Blessing, though that sounds like the kind of late-game nonsense that will never actually come up, whereas Gaeas Blessing messing up your Bone Dragon will come up
Noxious Revival (SPG) $29.99 Free spells are always worth looking at, but Noxious Revival isnt the most broken of these
But if time is the limited resource that is spent flipping sieges, players will probably prefer a more meaningful threat to reward them for that effort and hopefully end the game sooner
If you have access to a lot of mana, you can have really explosive turns with lots of Slivers going out against every opponent at the table