Cheapest priced copy (Fallout): $0.39 at Card Kingdom, near mint, their price list as of .
Lumbering Megasloth 
Creature — Sloth Mutant · 8/8 · Uncommon · Fallout · #80
This spell costs {1} less to cast for each counter among players and permanents.
Trample
This creature enters tapped.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.39 to $10.99 at Card Kingdom
2 rulings from Wizards of the Coast
- 8 March 2024The cost-reduction ability of Lumbering Megasloth doesn't change its mana cost or mana value, only the total cost you pay. Specifically, the mana value of Lumbering Megasloth is always 12.
- 8 March 2024Once you announce that you're casting Lumbering Megasloth, no player may take actions until you're done casting it. Notably, opponents can't remove counters from players or permanents to try to change Lumbering Megasloth's total cost.