Returning Mechanic: Changeling Kaldheim is a tribal-focused set, and Wizards has brought back the Changeling mechanic from Lorwyn block to support the new creature cards
History Create a Treasure token if that spell doesn't share an expansion symbol with a permanent you control or a card in your graveyard
Kraum, Ludevic's Opuss ability puts pressure on your opponents in two different ways: play more spells each round since the more they hold onto them to play later the more cards you get, OR : hold off on playing more than one spell a turn to keep from giving you any card advantage
For example, if your opponent is playing a Superior Spider-Man deck with Bringer of the Last Gift, you might consider a card like Rest in Peace or Ghost Vacuum as a hate card to stop your opponent's graveyard shenanigans
Being an instant will naturally play much better with the other instants in the deck, but also with this deck being incredibly fetchland heavy it might be difficult to keep two cards on top without having to shuffle one away before you have access to it
Being able to split the cost is a big help to take the edge off the high cost of Vessel but it is still a big investment