So I have been playing the Pokemon games on play.rom.online. I was wondering which of those Pokemon games has a hippopotas available if anyone remembers? Thats my favorite Pokemon to use in the games.

Ashton89000000 : I'm pretty sure it's Pokemon Rub/Sapphire/Emerald. Hope this helps.

Spidey243 : No it's not. Hippopotas didn't get introduced until gen 4.

Ashton89000000 : There are some Pokemon hacks that have Pokemon from gen 4 onward out there. I'd imagine that most of those would have a Hippopotas to catch.  I'm not 100% certain which games have hippopotas and hippowdon in them, I've played plenty of hacks, but my memory on which Pokemon appeared in some of them is kinda fuzzy.

accidental double post

They're available in every game starting gen 4 excluding Omega Ruby and Alpha Sapphire. In Diamond/Pearl/Platinum you can get it in the maniac tunnel. Though if memory serves me correctly unless you've caught a bunch of Unown they will be a fairly rare encounter (about 5%).

Other than that they're available post game in most Pokemon games onward judging from Bulbapedia. You can get them in the safari zone in HG/SS with the right terrain. It can be gotten as a swarm Pokemon (which is only possible post game) at route 4 in Black and White. I think in BW2 Hippowdon the evolved form is a swarm Pokemon in rugged mountain. X/Y is the only other games where you can get them before beating the Pokemon league, at route 9.

None of the main series games will have it. There are probably some hacks that make it obtainable though. Of the top of my head the ones I can think of is Pokemon Light Platinum and Pokemon Flora Sky which are both some of the most praised GBA hacks and are both touted as having all the gen 4 Pokemon included. They should both be on play.rom.online So those should make it obtainable somewhere along the way. There are probably many other hacks but I haven't played any Pokemon hacks in months so my memory is a bit foggy unfortunately. At least these two might give you something to go on to start with.