If your opening hand feels too weak, or is outright unplayable due to a lack of lands, you have the chance to take a mulligan and draw a new one that might be better
Whenever a commander I control attacks, Keleth, Sunmane Familiar gets a +1/+1 counter
You've also got Regeneration (Boneknitter), graveyard love (Corpse Connoisseur), graveyard hate (Crypt Creeper), life loss (Organ Grinder), tutoring (Corpse Harvester), edicts (Fleshbag Marauder), Necropotence variants (Graveborn Muse), and can even destroy the occasional enchantment (Quagmire Druid)
Set these cards aside to create a pile of bulk cards that you can sell all at once
If you don't have a copy of the card, change the filters to include Not Collected cards, search for the card, then click it
Their power was so great they were restricted or banned in most formats