Unless you're casting an Equipment spell this way, you must pay the spell's costs, and you must follow all applicable timing rules
Four mana, destroy all creatures, no scaling, life payment, or negotiation
With only four options to choose from, and all but one of them costing three mana, we're not really seeing a slam dunk here outside of Korlessa, Scale SingerKorlessa, Scale Singer
Angelic Overseer will also survive a skirmish with Acidic Slime
Coin-flipping as a mechanic is rarely used in Magic design, but it makes for good story moments, and therefore sneaks its way onto the occasional card
Players are unlikely to see new flip cards again, which is a shame because the space has more potential than the relatively underpowered cards that currently exist