Serperior

Serperior plays the simultaneous role of a Leech Seed staller and an offensive presence in 1v1. If Serperior can seed its foe first and survive a slower move, it will almost always win the matchup. This will allow it to beat Pokemon that prove unable to muscle past its respectable bulk in one turn, primarily Pokemon like Garchomp, Mega Metagross, and Magnezone, proving excellent in striking down bulky offense. This is further augmented by Serperior's use of Protect and Substitute to play mind games and bait potentially devastating single-use moves from Tapu Lele, Aegislash, and non-Flame Charge Mega Charizard Y. The usual weaknesses of fellow Leech Seed stallers, such as Jumpluff and Whimsicott—Taunt and recovery moves—do not necessarily apply to Serperior; thanks to its powerful Leaf Storm and Contrary, Serperior can muscle past Pokemon that attempt to mitigate Leech Seed's usefulness, allowing it to strike down Pokemon like bulky Mega Gyarados and Mega Sableye. Unfortunately, despite these advantages it holds over fellow Leech Seed stallers, it still falls prey to strategies that almost all Leech Seed stallers will lose to: faster, powerful attackers and sound-based moves. Common Pokemon like Greninja and Choice Scarf Porygon-Z will find no trouble in OHKOing Serperior, and noisy behemoths like Meloetta, Mega Gardevoir, and Kommo-o will bypass its Substitute and hit it where it hurts.