201-500.
Like others, I would do a general balancing with my time machine powers. I also don't really care about EDH, I'm just in it for theoretically giving cards a good cost-ability ratio. I'd nerf everything that is obviously undercosted to the proper cost. This includes things like Sensei's Divining Top (3 mana card) as well as overpushed mythic creatures like
Doom Whisperer and
Baneslayer Angel (both 7 mana cards).
I'd seek not to remove cards entirely:
Black Lotus is still an amazing card at 2 mana, and
Sol Ring that costs 2 and enters tapped is still a great card.
Brainstorm that only draws 2 cards and puts one back is still an excellent card.
Ancestral Recall becomes
Concentrate and
Time Walk becomes
Time Warp.
Demonic Tutor becomes
Diabolic Tutor . Moxes cost 1 mana each and ETB tapped (still insane cards). Sword of X and Y costs an additional 1 to equip.
Necropotence costs 2 life to activate. Ragavan either costs 2 mana, or drops a lot of abilities.
Urza's Saga's tutor ability now costs 1 to use.
Jace, the Mind Sculptor,
Wrenn and Six,
Teferi, Time Raveler, and
Oko, Thief of Crowns would all cost one more mana. And generally speaking, creature creep would be restrained for the most pushed cards.
Lightning Bolt is an interesting question. I think it's just a touch too efficient, but it's tough to change anything without throwing it totally out of whack. The best balance would be to have it deal you 1 damage, but I think I would leave it alone to keep the text box simple. Like
Force of Will, it's a card that serves to keep other cards in check.
Almost every mythic creature with pushed stats would also eat a nerf.
Carnage Tyrant ? Yeah right. 8 mana or drop the hexproof.
Grave Titan ? That's not how you balance 6 mana.
Emrakul, the Aeons Torn ? Not acceptable at any mana cost. It CAN be countered, and annihilates for 2 instead of 6. Still ridiculous.
Blightsteel Colossus ? Not acceptable at any mana cost. Make it an 8/8.
Hullbreacher abilities are a special case, and I suppose I'd generally limit it to only shutting off the first extra draw they would take.
I wouldn't really make any buffs. Nerfing cards gives room for a lot of almost-good cards to shine already. And old cards like
Squire were doing their best.
With my hypothetical balances, there would still be plenty of broken interactions all over the place. But there would not be cards intentionally printed to be more powerful than the mana they cost. 5 mana is 5 mana whether it be for a common or a mythic.
At this, the banlist on formats would need to be much smaller, but there would still be problem interactions that would need removed.
However I should say that these overpowered cards have always been a feature to driving hype and chatter around the game. If they game were more correctly balanced, it's possible it would never have gotten so popular.
