Kaldheim

Foretell - Similar to adventures in Throne of Eldraine, you would have your own individual zone for the cards you foretell, should you decide to add this mechanic to your cubelet.

Rune Cycle - Each seem fine, not too overwhelming for a cubelet. Could be a nice addition to an equipment/auras matter cubelet.

Snow - Snow is a house rule, but generally speaking, the lands produced from placing a card face down do not make them snow lands. Obviously, if you are building a snow matters cubelet, that rule can and should be changed. Cards listed in the set snapshot will not include cards like Ascendant Spirit because snow is not part of the basic cubelet.

Clarion Spirit
Cubelet rewards the ability to cast multiple spells in a turn later in the game, so this might be a nice way to reward and look to close out a game.

Divine Gambit
Exceptional answer to a lot of problems and adds a little chaos and entertainment factor. Punishing if opponent has no permanents in hand.

​Doomskar
Excellent boardwipe spell that can upgrade one of the other boardwipes, especially if adding additional foretell cards.

Halvar, God of Battle
If you have an equipement/auras matter cubelet, seems like a perfect fit, otherwise just a generically powerful card on either side.

Alrund, God of the Cosmos
Just the right level of entertainment without being too overly powerful.

Cosima, God of the Voyage
With a shared exile, this card would get passed around if people want to play that subgame. The Omenkeel won't exile lands, so you won't be playing anything with it in play.

​Egon, God of Death
With a shared graveyard, it could be well supplied to keep Egon around and the back side isn't overly powerful.

Valki, God of Lies
Relatively fair for the cubelet. Tibalt might be too powerful, but worth the test.

Tibalt's Trickery
Unique counterspell and with an entire deck full on nonlands, you are going to get your value.

Esika's Chariot
Fine vehicle to add to any cubelet that has a respect for artifacts and can answer it.

Sarulf's Packmate
Limited all-star that looks great in a Pauper cubelet.

Toski, Bearer of Secrets
Very annoying, but if you have exile effects, would be fun to add to the game.

Frija's Retribution
Decent way to close out a game or turn the game around.

Sarulf, Realm Eater
Pernicious Deed might be too powerful, but the conditions on Sarulf make it seem more manageable.