All you really have to do is avoid anything with global land destruction, no repeatable extra turns, dont intentionally get any 2-card infinite combos, and you cant have any game changer cards
If the copy is a permanent spell, it enters the battlefield as a token
Screaming Nemesis A 3/3 haste for 3 mana used to be very playable, but these days you need something else on that creature
Its also repeatable, unlike the blue equivalent sorcery or instant cards that give you a similar effect
However, with its need to spend Energy or be sacrificed, combined with its ability to sacrifice an artifact for 2 Energy and draw a card
One could argue that Jumbo Cactuar is not broken at all, and that there are already some very powerful cards that can single-handedly win a game even without 10,000 power, and that is true