Whether by casting huge Eldrazi or looping many spells, Omniscience is known to end games
It has Flying, which isnt unusual but then theres that ability text: You cant lose the game and your opponents cant win the game
A lot of EDH players run exile effects or ones that force you to sacrifice your permanents, and Ulamog is gonna get focused on quite a lot with that
That said, Zask, Skittering Swarmlord had one past spike back in November when Foundations released, but it quickly started to trend back down
There are plenty of other scenarios where either you dont have other creatures on the battlefield, they cant profitably attack, your Seafloor Oracle gets Lightning Struck before combat damage, and more where you wish your four mana creature in your aggro deck would have done more
They want folks to cast each other's spells to ramp with a mana in Treasure form, you too