Grubbernaut Deckling

Dark Bargain seems much, much worse than all the alternatives. Night's Whisper, Read the Bones, Dusk Legion Zealot, etc. 1 bolt/2 Tarfire seems wrong, as well

Tapped mana seems absolutely terrible in this deck, not to mention the problem of drawing a Forest when you didn't want it. We go through too many of our own lands to afford any second colors, IMO

5finga Scryfall is the best legality checker; unfortunately tappedout's is terrible.

5finga Fallen Empires is not a set that's considered for pauper legality.

"In this Magic Online format, all cards must have been printed at common rarity in a Magic Online set or product."

https://magic.wizards.com/en/game-info/gameplay/formats/pauper

This is the same reason Chainer's Edict is pauper legal, even though it never had a paper printing at common.

5finga Hymn is not pauper legal.