Manaphy

Manaphy's niche in 1v1 comes from its wide variety of utility options and EV spreads that make it a very flexible partner. As a Water-type Pokemon, Manaphy finds itself in an advantageous position against many of the common Fire-, Steel-, and Ground-types that occupy 1v1 such as Mega Charizard X, Heatran, Magearna, Zygarde-C, Landorus-T, and Donphan. Additionally, Manaphy's access to Grass-type coverage gives it good matchups against many of the top-tier Water-types in 1v1 between Mega Gyarados, Primarina, and Tapu Fini. Even with mimimal investment, Manaphy still has above average bulk, being capable of withstanding powerful attacks like Magearna's Twinkle Tackle, Garchomp's Tectonic Rage, and Choice Specs Naganadel's Draco Meteor. Unfortunately, Manaphy's strongest Water-type move is Surf, which means it often misses out on getting KOs, namely on non-Flame Charge Mega Charizard Y and Choice Scarf Genesect, that it would've gotten if it had a move with higher Base Power like Hydro Pump. Additionally, Manaphy's excessively balanced stats lead to it being required to sacrifice reliability against Pokemon it previously could knock out, withstand attacks from, or outspeed in the interest of gaining matchups against others. This is especially evident in the fringe scenarios of trying to make Manaphy reliably withstand attacks from Landorus-T and Naganadel while still maintaining the power and speed to deal with Mega Charizard X and Smeargle.