Rampaging War Mammoth
The crazy constelllation promo has a DPI of 1.3, which is lower than I expected at a buy-in of nearly $20, but its played in almost 15,000 decks so I could see it
This can be before blockers are declared, after blockers are declared but before combat damage is dealt, during combat after combat damage is dealt, during the postcombat main phase, during the end step, or, in some unusual cases, during the cleanup step
Still, played relatively early, I suppose that damage could open a path to take down its defense counters
7 Heroic Intervention Heroic Intervention is a fairly expensive but hugely powerful instant that can save an entire board state from destruction
You'll also make a Treasure to cast it, since you'll need that mana and there is no mana washing here, you have to use that mana