Valki's backside is a two-color planeswalker in Rakdos (black/red). His pack couldn't have the outrageous mana-fixing of Esika, nor the snow any-color ramp of Jorn.

I figured out that a perfectly reasonable pack could be made out of the 'cinderkin' elementals from Shadowmoor, because a whole lot of them use hybrid mana. You can use either a black mana or a red mana to play them. Plus, Manaforge Cinder is great at filtering mana to either black or red, allowing Tibalt or Kardur, Doomscourge to be played pretty easily. Oh, also, the cinderkin are badass fiery soot people.

I also let Tibalt steal an extra uncommon land. Why not? The Kaldheim 'realm-lands' are pretty bad overall, because a) you have to sac them to use them, and b) the activation always involves two pips of the land's 'off color'. The Immersturm Skullcairn might be good enough if health totals are low.