You may return any non-Avatar creature card or any planeswalker card from your graveyard to your hand with Overlord of the Balemurk's last ability, not just one you milled while resolving that ability
Admittedly, Abstergo Entertainment is probably too costly for a cEDH deck
This is the kind of awesome big-mana bomb that I love to play in Commander
For example, you cant sacrifice a Clue token to activate its own ability and also to activate Alquist Proft, Master Sleuths ability
Aethersquall Ancient Archipelagore Breaching Leviathan Charix, the Raging Isle Eater of Days Famished Worldsire Glacier Godmaw Grozoth Inkwell Leviathan Jokulmorder Kederekt Leviathan Kiora's Dambreaker Leviathan Nemesis of Reason Nimbus Swimmer Pearl Lake Ancient Segovian Leviathan Simic Sky Swallower Sin, Spira's Punishment Sin, Unending Cataclysm Sky Swallower Slinn Voda, the Rising Deep Starwinder Stormtide Leviathan Summon: Leviathan Thing from the Deep Trench Gorger Xyris, the Writhing Storm
You can play Archenemy in Commander easily
