Even if they manage to get a load of stuff back you are still good to go, your things will have haste, will be able to provide some mana and should be able to outright kill their whole board before attacking
If it was the target of any spells or abilities, it still will be, although it may or may not now be a legal target
This is a pretty hefty number of new legendary creatures for a single Universes Beyond set (although the Commander-specific Fallout added 53, and Lord of the Rings added over 100 across both the main set and Commander precons)
This is largely in part due to the Elvish Empire preconstructed deck functioning as a great on-ramp to this powerful tribe, featuring a sizable number of Elf-tribal staples and a powerful Golgari (black/green) spin on the traditionally mono-green tribe
If this card is in your early hand, you can also use the dredge mechanic to quickly build your mana pool and ensure you don't miss crucial land drops