Hey, I've been brainstorming a couple of ideas for this format and ... well, you're the only other people I know that have ever played it, so I'd love your thoughts.
We're finding that cards that exile just feel too powerful. You're removing a substantial piece of the opponent's deck, and also removing them from future redraws, which feels too good. Exile mechanics like delve, collect evidence etc are also way worse to being basically unplayable without some way to get those cards back. Same with red's 'exile the top, play it this turn' type of stuff.
Here are a few suggestions we have to overcome it:
1) When you pay the 3 life to shuffle the graveyard into your library, you then move the exiled card(s) into your graveyard. I like that this lets you eventually re-use the cards and it's probably the most practical, but it could be exploited by (for example) reanimation, delve, etc by looping things in and out of the graveyard.
2) When you pay the 3 life to shuffle in, you then put the exiled card(s) on the bottom of your library. This gets around any graveyard shenanigans you could exploit above, but doesn't work as well if the deck is small in the late game, meaning you (again) can get things straight from exile to your hand if it's the only card in your deck.
3) Any 'exile' cards you play will exile themselves too, so they both become one-offs. This preserves the permanence of exile removal while balancing it out, although it doesn't work as well when it comes to things like delve effects, red's impulsive draw, etc.
4) Any exile cards you play go on to the battlefield as permanents, and work like Oblivion Ring. For example, 'exile target creature' removal will become an enchantment on the field, effectively removing them both from the gameplay loop, but if a player can remove the enchantment, the card goes back to the battlefield and the spell goes to the graveyard. The idea here is that we never want anyone to be able to pay 3 life to get back cards exiled by things on the battlefield, but this is the wildest suggestion here.
Nothing feels quite right, and we obviously have to test which works, but didn't know if anything stood out as immediately obvious to you?
I also think we're going to make the 3-life-to-shuffle a sorcery speed ability, partly to balance the above and partly because we find life gain is at a premium in this format because of it. Being able to do it at less-than-optimal times will help.