4th Gen What should I do with HeartGold?

(I messed up the title, if anyone who has the power to change it can, please change it to 'What should I do with HeartGold?')

Fourth Gen has always been my favorite, (especially the Johto remakes) for the longest time because I've always had an artsy eye, and the colorful and well-done sprites as well as being able to walk along my favorite Pokémon really spoke to me.

Six years after the release, I want to play the game again. I just finished replaying the main game in PMD Explorers of Sky (Phanpy and Eevee were my Pokémon by the way, REALLY hard combination to pull off) and I had a craving to play a main-series game suddenly. I dug through my options, and they were Platinum, HeartGold, Y, FireRed, LeafGreen, or Ruby. I decided upon HeartGold, because it's honestly my favorite.

So what I'm really wondering is, what should I do? I've already played the game, I've already defeated all the Gym Leaders, and Red, I don't think it'd just be fun to play the game in it's entirety again. I don't really want to do a Nuzlocke either. What's something I could do that's fun? Perhaps play the game with a custom set? With the Pokémon from Explorers of Sky, like Dusknoir, Wigglytuff, Grovyle, (damn that one scene where SPOILERS )

So I don't know, what do you all think? What should I do?

Did you already catch Kyogre and Latias? You could always try to go through with one type of pokemon. Water would probably the easiest.

if you don't want to restart it you could just play in the pokeathlon. i spent hours doing that tbh.

honestly though i usually just start over for fun. maybe try doing a themed team as i do that often based on my mood. you could challenge yourself and try an all one type team. on hg/ss specifically i remember doing an all rock team and an all bug team. the bug team was difficult.

Maybe you can try collecting all the Pokemon with the Pokegear's Hoenn and Sinnoh Sounds, as well as the Safari Zone and its customization that can allow for new Pokemon to appear, some of which you may have to wait a while for.

Ayselipera's suggestion to do the Pokeathlon is something you can try as well, since it can be a good sidequest to try, and the points you receive can be used to buy Apricorns and items for evolving certain Pokemon.