I am working on this concept for one my groups to explain how monsters/aliens/monsterfied ponies could come to Equestria.

While I was thinking of using some sort of interdimensional portal, I don't want it to be too cliche.

So I thought I would try to ask this question here and see if any of you had any suggestions.

Well, let's see...
(a) They could arrive on a boat from another continent.
(b) They could have been hiding inside Equestria all along.
(c) Maybe they were on the moon? Or in Tartaros or some other canon hiding place for evil?
(d) Space ships
(e) Time travel
(f) Interdimensional portal
(g) Alternate timeline (this is pretty cliche for FIM fanfiction tho)
(h) Created (accidentally?) by a magical spell
(i) ...or a disease or parasite or something
(j) They were always there but normal ponies' memories of them were all erased so they thought they'd just shown up. q:3

6469238 I mean I want to go the portal route but I don't want to be too cliche. Originally I was thinking of having the portal being created by a strange mutation in some plunderseeds that somehow resulted in the vines forming a gateway.

one thing I have yet to see explored for vamponies is changelings experimenting with ponies trying to make ponies more like them to be a kind of slave race, thus vamponies were born/created.

Honestly portal stuff and alternate universe stuff have already been explored somewhat with canon... so really nearly anything is fair game.

6469226
Randomly-forming portals that just so happen to lead to X place are overused, but so are portals in general.

And that doesn't matter. It's the execution that decides whether an idea is original or cliche, and every idea has been done a thousand times before.