While exiling your own creature is generally frowned upon, youll be gaining yourself 10,000 life, which is a huge amount in any game
As seen with Dredge, we all know what happens when the graveyard becomes an extension of its users hand: you can mill your deck to draw cards and then cast them for the Flashback cost, to say nothing of getting a second use of removal and bounce spells that can massively interfere with your opponents strategy, particularly if theyre running a creature-heavy deck
Agent is also notorious for bringing games to a grinding halt as you search through a one hundred card deck you're unfamiliar with
You either create cards that just objectively suck (i.e.: most of this list), or you risk making an actual good leyline that breaks the game by nature of how these cards work
Standby Phase This is a Phase used by monsters, Spells, or Traps that need preparation