The payoff you get just from this card alone is enough to make me think that youd strongly consider expanding into Grixis colors if you already have a demon tribal deck
Krark, the Thumbless leads to funny, coin-flippy games, at least until you bust out cards like Spark Double and a partner commander like Sakashima of a Thousand Faces to start breaking things
As long as it sticks around, your creature spells cost less, which helps you in a big way
So now the taxes (since theyre all relatively the same Ill keep this brief) Propaganda , Norns Annex , and Windborn Muse are all Ghostly Prisons (although Norns Annex will most likely drain your opponents life rather than tax them on mana
"Watch live: Pokemon World Championship 2018 in Nashville"
Kellen offers a powerful reward for doing a specific thing, but also gives no means of doing that thing himself or enabling it at all