Nintendo has already taken it to the next level
https://www.nintendolife.com/news/2021/01/nintendo_is_buying_luigis_mansion_studio_next_level_games

Haha, lol

If Nintendo was to buy a any third party company. The only logical one in my opinion would be platinum games because they're the one who work closely with Nintendo.

IMO Hal Labs would be the kind of purchase Nintendo makes.  Kind of like Next Level, closely tied to Nintendo over the years, makes great games for their systems, and had “Nintendo DNA”

HAL is safe bet I think. Platinum makes hits and misses so they are risky. Bayonetta and Astral Chains were really high quality series, whereas Starfox Zero and Wonderful 101 were duds imo. Too risky for Nintendo, as much as I'd love for them to utilize Platinum on other ips they already own.

They overpaid.

This is only funny because Nintendo are at the top of their game. People forget Nintendo had and lost (or came close to losing) the biggest 1st party RPG, platformer, racer, fighter, shooter, sports games but reclaimed the crown eventually. Did anybody ever think Splatoon would go on to beat Halo?

I think SF: Zero's main problem wasn't necessarily Platinum's fault. From my understanding they wanted to be more ambitious, but Miyamoto really reigned them in to focus on what he thought SF should feel like in the modern era. If they had more creative control that game would have been way better, in my opinion. But still, it is a stain on their record, as is the canceled Microsoft dragon game and W101.

Their best formula, the one they are known for the most, is action games with amazing foreground/background sequences going on while fighting. They are stunning in that department, and I think there are definitely family-friendly IPs Nintendo owns that Platinum could make stunning games using that formula. Kid Icarus in a Bayonetta-style game would be flipping awesome! Metroid Other M would have been far better with Platinum doing it too, since that was also a 2.5d kind of game. I could even see them doing a crazy action-packed Donkey Kong game, or some other ips Nintendo hasn't touched in a while.

Obviously, they'd still be free to do their own ip games they have now, or even make new ones, but Nintendo's catalog is crazy and they'd make better selling games with their ip. The Dynasty games have never sold better than when using Nintendo ips. The Total War series REALLY took off when they made games based on Warhammer. Using popularly established ip as a base for a game style they are really good at making would bring Platinum a lot more success than they've had (and they've had quite a bit of success).

If you can't get the best third party games, then just make a first party game that appeals to a similar crowd and crush those puny third party studios! Nintendo likes to really experiement and make 2-3 new ips each generation. Most of them have moderate to decent success (1-2 Switch, Arms, Pikmin), but every now and then they strike gold (Splatoon) and it can really expand their appeal and base sales into new areas.

Nintendo doesn't need to and most likely never will buy studios like HAL and Intelligent Systems. HAL is already situated within Nintendo's HQ and might as well be Nintendo. Intelligent systems is Nintendo's longest partner of 40 years. And I don't see why Good Feel, Camelot and Grezzo would abandon Nintendo.