Big Mother Mouser Dragon Broodmother Duskana, the Rage Mother Elesh Norn, Mother of Machines Faerie Guidemother Faerie Guidemother Grandmother Ravi Sengir Grandmother Sengir Hit the Mother Lode Hydaelyn, the Mothercrystal Ishkanah, Broodmother Mother Bear Mother Kangaroo Mother of Goons Mother of Runes Mothers Yamazaki (playtest) N'Yami-Class Mother Ship Phyrexian Vatmother Queen Mother Ramonda Rug of Smothering Sakiko, Mother of Summer Sliver Gravemother Sliver Queen, Brood Mother Smother Smothering Abomination Smothering Tithe The Goose Mother The Motherlode, Excavator Wort, the Raidmother
missing the drop shadow, they might be worth something
That alone is pretty powerful, but I would say it is even more relevant for the fighting types than others, as they typically require a ton of energy in order to execute their attacks
River Kelpie Primarily a payoff for mechanics like persist or undying, River Kelpie provides card advantage whenever permanents enter the battlefield from the graveyard