Elite Four: Rival
The circle is now complete. Your first and last challenge is with your rival, and he'll have just as many tricks as ever to face you. With a fully rounded out team you'll be hard pressed to find one Pokemon to take everything out; however, if you don't mind legendaries, I recommend Zapdos for its Electric-type (good for beating literally up to 2/3 of the team depending on who he chose, or at the very least half) and Flying-type (provides STAB and good speed to take out Alakazam with a quick physical move). If not, balance everything out as always: don't train just one Pokemon (seriously don't) and make sure your type coverage is astute. His team has a few flaws you can exploit: Arcanine, if he has it, laughably knows Ember as its Fire-type attack, Gyarados's Hyper Beam makes it stall a turn if it doesn't wipe you out, Exeggutor only has three attacks (both damage-inflicting ones of the Normal-type), and Rhydon has a low-accuracy OHKO move it'll try on you. An alternate approach to this is to just use Toxic on everything (use PP Up if you're doing this) and stall it out with Chansey or another bulky Pokemon. It's not exactly enthralling but if it's what works go for it. Good luck!