Building a Commander deck from singles means tracking down 100 individual cards across multiple sellers, waiting on separate deliveries, chasing missing parcels, and hoping nothing arrives damaged
Rowan makes cards that are already extremely strong such as Ad Nauseam and Bolas's Citadel EVEN STRONGER by making each drop of blood you pour into them discount your eventual game-winning spells, or even value pieces or tutors you might play along the way to secure your winning lines
The starter decks for debut set The First Chapter each had their own ways to win, whether by rushing to get the most lore, holding back your opponents or getting lots of ink down for big characters
Equip Helm to Celebrant, make a new Celebrant on combat, attack and exert it, then repeat the process during your extra combat
Bosh, Iron Golem Bosh, Iron Golem is a classic commander, but a little over-costed