Plus his mana can be used for things when you don't have any creatures out to play with, whereas Sarkhan's +1 and -2 really do require a certain creature-fueled board state, but Domri can always lean on making mana or using his 2nd ability even when there are no creatures on the battlefield
Remember that you can choose if you want to return Narcomoeba from the graveyard or not
How To Play The Deck A Sephiroth, Fabled SOLDIER Commander deck is constantly sacrificing its own creatures, burning your opponents with Sephiroth's effects and other permanents that have similar effects
For example, even if we interpreted your library as part of the battlefield for this purpose, slipping one into the card sleeve of a card in your library during a search effectively marks your deck, and that's not allowed
Sometimes players may have to cut some of their favorite cards in order to keep the total number down, so deciding which cards go best with each other is key