Arc Lightning

In Commander, Arc Lightning occupies the low end of playable — token-heavy tables give it real work cleaning up multiple small blockers or pinging planeswalkers, but at three mana it competes with strictly better removal like Chaos Warp and Swords to Plowshares. In Pauper, the common restriction narrows the field enough that splitting damage across multiple targets has genuine appeal in red aggro or burn shells. Legacy, Vintage, and Modern all offer far more efficient burn, so Arc Lightning sees essentially no play there. Pioneer falls in the same category — the format has enough redundancy that three mana for three damage never makes the cut.