Firstly; I could have sworn that we're supposed to come up with a team type before deciding the next member.
Secondly; *pats Scyther on the back* It's an honor to be nominated, buddy.
Thirdly; Qwilfish would most likely the best choice if we decide for spike-stacking offense, or phazing-based stall. But, if we decide on a team type other than those two (I.E. A team that takes advantage of Meganium to provide set up opportunities), than a slot solely for the express purpose of Spikes and counter a few things that, down the road, may not even threaten us could be a waste of slot. I'm not berating Qwilfish, it would form a nice defensive core with Meganium, I'm simply saying that it may not be worth the trouble later down the road.
Therefore, I'd like to propose this.
Kabutops @ Life Orb
Trait: Swift Swim
EVs: 4 HP/ 252 Atk/ 252 Spd
Jolly Nature (+Spd, -SpAtk
~ Swords Dance
~ Rapid Spin
~ Stone Edge
~ Aqua Jet
What does this set do? Meganium is grounded, which means it is hit by Spikes. Also, there are several spikers who carry a super effective STAB(Accelgor, Scolipede, Crustle, Qwilfish(though use of a Poison STAB is uncommon, I'll admit)), so a Rapid spinner able to take on three out of four with Stone Edge is good. He also has somewhat decent defensive synergy with Meganium. He attracts electric, grass, and ground attacks that Meganium can switch into. Meganium can attract fire and ice attacks for Kabutops to switch into and get a Spin or SD off. Aqua Jet provides priority, which would be helpful with Hitmonchans who may try to revenge kill you with Mach Punch (The whole point of using Jolly it to outspeed a max speed Hitmonchan), assuming you predict right and SD. Otherwise, you'll only get a 3HKO, while max Atk Hitmonchan scores a 2HKO.