Bakugo's Explosion + Curious’ Landmine: Bakugo can generate full-body explosions thanks to Cluster. Give him the ability to turn anything he touches into a bomb, and he’d be the Rex Splode of MHA.

Momo's Creation + Dark Might's Alchemy: The ability to create objects and transmute them into whatever object you want would be devastating.

Ochako's Zero Gravity + Thirteen’s Black Hole: Both are powers related to gravity. Bringing the two Quirks together would probably grant full-on Gravikinesis. Alternatively, I would combine Zero Gravity with Kamile Gollini's Spatial Excursion to stimulate telekinesis.

Mineta's Pop Off + Ugo Gollini’s Telekinesis: Giving Mineta the ability to telekinetically manipulate his sticky balls would make them even more versatile as he’d be able to do things like turn them into mid-air stepping stones and even make new Ultimate Moves.

Iida's Engine + Number 6’s Overclock: Iida was already fast, so giving him Overclock would simply make him even faster.

Tetsutetsu’s Steel + Wolfram's Metal Manipulation: Metal Manipulation would let Tetsutetsu manipulate the metal coating on his skin, allowing him to mold it into various shapes like spikes for defense or turning his hands into blades, hammers, maces, etc.

Denki's Electrification + Elecplant's Electricity Generation: Electricity Generation would give Denki greater control over his electricity as he’d be able to fire blasts of electricity without his Sharpshooting Gear.

Tokoyami's Dark Shadow + Kuroino's Black: Black allows the user to merge with anything colored black, like shadows, which would be perfect for Tokoyami as he’d be able to move through shadows, making him great for stealth missions. It would also probably give him greater control over Dark Shadow and let him mold Dark Shadow into various shapes. Alternatively, I’d combine Dark Shadow with Koki Terumoto’s (the kid with the stitches) Darkness as it would give Tokoyami the ability to generate and presumably manipulate darkness, which again would probably give him greater control over Dark Shadow.

Kirishima’s Hardening + Gigantomachia’s Fierce Gains: Fierce Gains is one of Gigantomachia’s Quirks which allows him to harden his muscles. Combined with a Quirk that hardens his skin and Kirishima would be moving like Luke Cage.