The main card that really powers the World Eater is Nykthos, Shrine to Nyx, as it produces an excess amount of Green mana to effectively activate the Hydra's monstrosity ability
With an appropriate outlet Walla effectively has flash which is a nice little trick
First, my take on Mardu Reanimtor, which has a very different philosophy from Storytimes: Creatures (22) 4 Imperial Recruiter 1 Ashen Rider 4 Seasoned Pyromancer 1 Skyclave Apparition 4 Grief 4 Priest of Fell Rites 1 Young Necromancer 2 Archon of Cruelty 1 Vile Entomber Lands (22) Spells (16) This plays a more value-oriented, disruptive game than Storytimes take on Reanimator
Like most big green spells of its kind, it exiles itself as part of the spells resolution
And as with any other mass token-producers on this list (or otherwise), that translates to a ton of valuable triggers from your tribal support cards
Rebbec, Architect of Ascension is just the right pairing to help with that because Silas Renn is an artifact creature