I’m probably late, bit I’d like to propose
the following ᴾⲕᴹⲛ species to be featured
inside the Easter Holiday Cave
(or the next ones alternatively 
).
Nosepass 
Based off Moai statues. Mostly proposing this as an inside joke on “Easter Island”,
named thusly due to the date it was discovered by European navigators.
Bronzong
In France, chocolate eggs are brought by bells rather than the easter bunny.
Well, the bunny is also spreading, but still.
And yes, I know bronzong is a dōtaku bell, but that’s still somewhat fitting taking into account the fertility thing and the legend accordingly to which it originally was a monastery bell.
Sunkern
Easter is about birth&rebirth, thus eggs have been a thing for centuries.
Seeds are, like eggs, symbols of birth or rebirth, plus sunkern has a sprout growing atop.
Exeggcute, torchic & the chansey line are very fitting,
but chances are the fan-devs already thought of those.
Possibly phantump because in heraldry stump w/branch = new life sprouting from the old, but again, might look a bit too spectral for an Easter event.
Thank you very much indeed for your time, have a good day/night!
