Energy advantage is one of the most important things in Pokemon, and having a card that keeps all your Energy in play is so good
This is fine for us as a vast majority of our plays involve monsters that are already of the Zombie type, however if our opponent is not running a Zombie Deck, well tough luck they will be unable to make any summons as Zombie World only makes the monsters on field or graveyard Zombies, not the hand or Extra Deck
So, you think you've got some good card cards
As a final note on attack damage power creep: while almost everything related to power creep is only worth discussing when talking about relative power creep, there is one worthwhile thing to mention
It's also able to manipulate where other creatures exit, an ability it can employ to help other cellarspawn track down their prey or trap a survivor in an endless loop of rooms with no escape
And because this ability triggers upon entry, you don't have to particularly worry about keeping Trishula safe since you'll have already made good use of its effect