It's currently one of the format's tier 1 decks, with a 6.5% metagame-wide share and numerous high profile finishes at major events
Both of its mechanics are very strong
Well, now its just silly, isnt it
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
Furthermore, while the healing isn't as great as a Venusaur ex and Butterfree deck, the high HP values of Dialga ex and Arceus ex make the 10-20 HP heal each turn a nice bonus
Then as this explores you'll draw lands or toss +1/+1 counters on this to grow it over time, and did you note the word missing here