Sundial of the Infinite

The clean answer to a problem most players never knew the rules created: what happens to a delayed trigger you do not want to resolve. Ending the turn on demand exiles everything off the stack, which turns the card into a one-mana eraser for your own pending costs and downsides. The key targets are delayed triggered abilities, the "and then" clauses that wait on the stack until an end step. A "sacrifice this creature at the beginning of the next end step" trigger from a sneak-into-play effect, a "return this to its owner's hand" promise tacked onto borrowed permanents, a "pay or lose it" tax queued for later: let the trigger go onto the stack, then end the turn and exile it before it resolves. The activation restriction (your turn only) is what keeps this from being a universal Stifle; you cannot snuff an opponent's spell on their turn, so the card lives entirely inside your own engine, scrubbing the strings attached to your best effects. Where a counterspell answers a single threat for a fixed cost, this answers an entire category of clauses with one repeatable activation, which is why it reads as a toolbox piece rather than interaction. The cost of that flexibility is collateral: ending the turn also expires every "until end of turn" duration, discards you to hand size, and skips your own beneficial end-step triggers, so it is a scalpel you have to aim. Its value lies in the events it prevents from ever happening.