Sage of the Inward Eye

Commander is where Sage of the Inward Eye actually gets to do its thing — spellslinger commanders generate the volume of noncreature spells needed to make lifelink triggers matter, and a wide board turning lifelink on and off each spell creates compounding life advantages that close games. In Legacy, Modern, and Pioneer, a four-mana creature that doesn't impact the board immediately is simply too slow; those formats kill before the effect accrues value. Vintage has the raw spell density to abuse it, but there are far more efficient engines available. Oathbreaker sits closest to Commander in spirit, and a spells-matter planeswalker paired with Sage of the Inward Eye as the signature spell slot could produce real results in that format.