I don't know how frequently these events are distributed in Brasil, but if you have your doubts, you can just try to trade the mons you want the most with someone, or just use the Pokebank (although that's a paid service).

Kinda sad to delete this person work, but maybe he shouldn't have sold it. I would at least try to save the legendaries

I would keep the game untouched and buy another copy.

That is why you'll buy another copy =p then latter you can get the legendaries and shinnies you want.

Leave the save intact, buy another version of the game to play yourself. The copy you hold with that save is probably worth fsr more than you paid for it.

With a second 3DS and a second Pokemon game (don't forget this) you can trade with yourself and so switching Pokemons between games. This is why also a physical Pokemon game is preferable to a digital, because you can put it in the other 3DS.

Without a second 3DS though, the only way to transfer Pokemon is to my knowledge Pokebank. You have to pay a yearly fee, which is here in europe 5€. Your Pokebank-account is linked to a Nintendo Network ID. Don't know if it is the same your 3DS is linked to, but I assume that is the case. Games you can connect Pokebank too are X/Y, Omega Ruby/Alpha sapphire, Sun/Moon and Ultra Sun/Moon. As there is no Switch-Pokemon so far it is unclear if Pokebank is the way to go on Switch too, or if they use something else to transfer Pokemon from your 3DS-games to your Switch games. For Black/White a different app is used to transfer Pokemon into the newer games. With Pokebank you transfer directly between in game Pokeboxes and your online boxes (which are 100, so saving overall 3000 Pokemon).

Eventy include physical events which may or may not happen in brazil and online events, which means you connect your game in a time-frame to the internet. Don't know if Nintendo restricts the online events per region or not. Also Pokebank from time to time gifted me Pokemons (nothing super-special, last time I got the evolved version of the starters of Sun/Moon). Again I don't know if these Pokebank-gifts are region bound.

Send it to a museum as an exhibit. I heard your country might need new ones. This one certainly seems old, rare and precious.

That person put in +400 hrs with tons of extremely rare pokemons in the game only to sell it away.......dam, that person must've given up on Pokemon.

Listen to what Ka-pi said and get bank. It's $5 USD and lasts for a year, and even if you let your sub run out, it keeps your stored Pokemon in the meantime. Anything you want to transfer over to your new game, you can do so at your leisure.

As far as how to tell if a mon is hacked, there are definitely ways you can tell. The online checker looks for these things: illegale stats, illegal moves, and symbol representing what game (aka region) the Pokemon was born/generated. So long as you don't have a Pokemon with stats that can go past the max at its current level, a move it can't possibly ever learn (event Pokemon complicate this a little), and doesn't come from a region that it couldn't possibly have been available, you should be fine. You can go to Bulbapedia and look up all this info for any mon, and I'm sure there are online sites that let you plug in your mon's info and have it tell you if it's legit.

Otherwise, the online checker is notoriously easy to beat. Word of advice: the people wonder trading you shiny legendaries and battling with a team full of six shinies with maxed out stats and egg moves - they're hacked. Most people are either using hacked mon, or using hacked mon to breed legit ones (that's what I do, 6IV Ditto here). To get caught for hacking and banned is equivalent to tapping a police officer on the shoulder, knocking coffee out of his or her hand, then punching a woman in the face. You have to really be trying.`So in all likely hood, those mon you inherited came from hacked means in some way, but I bet they are fine. If you see a Charizard with Hydro Pump or something, then that should be setting off red flags in your head, lol.

Also, the thing you REALLY want to be careful about is not losing rare items. PokeBank does not allow you to transfer items. There was an even early in Y that gave people access to Blazikenite (Blaziken's mega stone) that was not originally in the game, and there is no other way to get it if you lose it, other than trading with someone else. You don't want to lose that, so if you do restart your game and you have it now, make sure to ask someone to temporarily hold it for you. Same thing with either Pinsirite (Y comes with Heracrossite, X comes with Pinsirite).

And certain berries could only be self-obtained by playing certain mini-games online that are no longer available, like the Custap Berry. Definitely have someone hold onto that for you if you have it now. I keep trying to end this post, but I keep thinking of more things, lol.

Wow that's a lot.  I can understand not wanting to touch a Pokemon in awhile after playing so much of it but you wouldn't get rid of the game completely like this seller did would you?