Cheapest priced copy (Fallout): $0.49 at Card Kingdom, near mint, their price list as of .
Elder Arthur Maxson 
Legendary Creature — Human Knight · 4/2 · Rare · Fallout · #413
Creature tokens you control have training. (Whenever a creature token you control attacks with another creature with greater power, put a +1/+1 counter on that token.)
Blind Betrayal — Sacrifice another creature: Elder Arthur Maxson gains indestructible until end of turn.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.49 to $3.49 at Card Kingdom
2 rulings from Wizards of the Coast
- 8 March 2024A creature’s training ability triggers only when both that creature and a creature with greater power are declared as attackers. Increasing a creature’s power after attackers are declared won’t cause a training ability to trigger.
- 8 March 2024Once a creature’s training ability has triggered, destroying the other attacking creature or reducing its power won’t stop the creature with training from getting a +1/+1 counter.