Theft is a key part of the blue/black Dimir decks (though it has spread to other colors) and is a very fun, if notorious, way to play Commander
Kefka, Court MageKefka, Court Mage Speaking of grindy, Kefka, Court MageKefka, Court Mage strikes me as the long sought-after commander for a more traditional grinding game plan for a cEDH deck
To take advantage of its need to see your opponents bleed, running other Bloodthirst-y cards, like Petrified Wood-KinPetrified Wood-Kin, Furyborn HellkiteFuryborn Hellkite, or some spectacle cards like Light Up the StageLight Up the Stage, add some good support
If you enjoy swinging tempo with one play, Gisa is a great pick
Even if you just draw three cards it is a slightly more expensive Harmonize, another popular green draw spell
Legality depends on the tournament format -- Enduring Courage can be legal in some formats and banned or restricted in others