Jack-o'-Lantern

In Commander, Jack-o'-Lantern earns a slot in artifact-synergy decks — commanders like Breya, Etherium Shaper or Urtet, Remnant of Memnarch want cheap artifacts that replace themselves, and the looting ability at instant speed is genuine card selection rather than pure cantrip. In Pauper, it competes in artifact-based combo and Affinity shells where every zero- or one-mana artifact with a body matters, and the ability to trade a card for colorless mana in response to a threat is occasionally relevant. In Modern and Legacy the bar is simply higher — Mishra's Bauble and Urza's Bauble both cantrip for free, so Jack-o'-Lantern's one-mana entry and conditional mana ability don't justify the slot except in dedicated artifact-count shells. Pioneer represents the most plausible competitive home outside Pauper, where the artifact creature type and the looting-for-mana mode can support specific combo infrastructure.