Felothar, Dawn of the Abzan

Felothar, Dawn of the Abzan is legal across every major constructed format but is firmly a Commander card — the counters payoff requires a critical mass of enters-the-battlefield creatures and recursive loops that 60-card formats can't reliably assemble before the game ends. In Standard, Pioneer, and Modern, a five-mana legendary with no immediate protection is too slow without a dedicated shell built around it, and no such shell has emerged. Commander is where Felothar operates at full power: the longer game, the singleton-fueled variety of counter synergies, and the natural home in Abzan +1/+1 counter or graveyard-recursion builds make it a legitimate engine piece rather than a curio.