I don't know Aizen quite as well as I'd like, but... according to our page on him, "He can only use his Reality Warping when possessing the Hyogoku."
I don't know what Reality Warping specifically he has, nor if he still qualifies as having 7-B stats when possessing the Hyogoku, sadly.
That said, Kyōka Suigetsu is a big boon to Aizen here. With it, his hypnosis lets him control all 5 senses of his victim, & it still works whether they know they're hypnotized or not.
With this Meganium pretty much has no means of detecting or keeping track of Aizen, unless pain isn't one of the controlled senses -which I doubt- & Meganium can think to use where it's hurting from Aizen's attacks as a basis for what direction to attack.
There's also the fact that Aizen has Pseudo-Flight, giving him a mobility advantage, & meaning there are a lot more places Meganium could attack & have Aizen NOT be, which, combined with the hypnosis, means in theory, it won't hit him very much.
But, for the sake of argument....
Well, Meganium DOES have some tricks up its sleeve....
http://bulbapedia.bulbagarden.net/wiki/Meganium#By_leveling_up
For one, does Kyōka Suigetsu count as a status ailment? If so, Safeguard may be able to block it. But that assumes Meganium thinks to use it before it sees Aizen's sword/Aizen himself, depending on which it is for this form of Aizen's.
Similarly, if Meganium has Leaf Guard & the weather has heavy sunlight (The former is possible, the latter might be unlikely/unfair.) it's protected against status ailments altogether. Heavy sunlight will also mean Meganium heals itself more whenever it uses Synthesis.
Then there's Poisonpowder.
| SM | The user scatters a cloud of poisonous dust that poisons the target. |
Assuming it's used early enough, Aizen lets himself be in range of it, or it's just too difficult to avoid, Aizen could end up poisoned.... I mean, assuming he doesn't use a Barrier to block it, or an attack to destroy it or somehow redirect it, besides dodging it.
If he has Regenerationn in this form, Aizen's regen might combat the poison a bit, if he does get afflicted.
If Aizen is stupid enough to stay in range of Meganium, it could Body Slam him, for a small chance of inflicting Paralysis.
As for combatting during the hypnosis, as opposed to hoping it's a status ailment itself.... Meganium has:
http://bulbapedia.bulbagarden.net/wiki/Petal_Blizzard_(move)
| Games | Description |
|---|
XYORAS
SM
| The user stirs up a violent petal blizzard and attacks everything around it. |
|
Even if Meganium is being completely deceived in all 5 senses, unless Aizen can use KS to directly & completely control everything Meganium does, attacking everything around it may be a way of assaulting him while under the hypnosis.
Of course, he still has the options of dodging, putting up barriers or defending against the attack, although it might catch him by surprise. He could also try to fly out of range of his grounded opponent.
Another option is:
http://bulbapedia.bulbagarden.net/wiki/Magical_Leaf_(move)
XYORAS
SM
| The user scatters curious leaves that chase the target. This attack never misses. |
Again, as long as Meganium controls what it does, this may also be a feasible form of attack, as the leaves chase Aizen; If they move independently of Meganium, this homing attack may be a means of hitting him.
With Sweet Scent, Meganium can reduce Aizen's evasion....
http://bulbapedia.bulbagarden.net/wiki/Sweet_Scent_(move)#Descriptio
Although its most recent descriptions mostly focus on that it's a sweet scent that reduces evasiveness & attracts wild Pokemon, it's earlier descriptions give more flavour.
| Stad2 |
A pleasant aroma that distracts the target, making the opponent easier to hit.
|
RSE
'Colo.'XD
| Allures the foe to reduce evasiveness. |
Presumably, Sweet Scent could be used to distract or allure Aizen himself, making it a bit harder for him to defend, wherever he is.
And Meganium has access to both Reflect & Light Screen, which can halve physical, & "special" damage, meaning it can halve the damage from just about any of Aizen's attacks.
It can cure statuses it has via Aromatherapy, although, that will also cure Aizen's statuses, & depends on Aizen letting it smell the aroma, if he has it under KS, even if Aizen might not know what the aroma does.
And of course, Synthesis offers it healing.
Meganium's ability Overgrow boosts the power of its offenses when it's "in a pinch". Mechanically, for what it's worth, Overgrow triggers when Meganium is below 1 third of its max HP, & boosts power with Grass type moves by 50%.
Lastly, it's possible Aizen may have trouble bringing himself to fight Meganium, if we go by this Pokedex entry:
| Emerald | The fragrance of Meganium's flower soothes and calms emotions. In battle, it gives off more of its becalming scent to blunt the foe's fighting spirit. |
|---|
In short:
Using Safeguard early enough, or being in heavy sunlight with the Leaf Guard ability are means of protecting Meganium against statuses. This could be trouble for Aizen if his KS hypnosis qualifies as a status.
Similarly, using Aromatherapy & smelling the aroma -if Aizen lets it/doesn't realize he should prevent it- cures status ailments. It will also cure Aizen's status ailments.
Body Slam could Paralyze Aizen giving him a small chance of becoming immobile from being "fully paralyzed" sometimes. This depends on him being in range of it, though.
Overgrow boosts Meganium's power with Grass moves when its "in a pinch"/low on health.
Meganium can use both Reflect & Light Screen to halve damage from just about anything Aizen can throw at it. Reflect halves physical attack damage, Light Screen halves "special" attack damage.
If Meganium can poison Aizen with PoisonPowder, it can help wear down Aizen, or help combat his Regenerationn, if he has it in this form.
Meganium can use Synthesis to heal, which heals more if there's heavy sunlight.
Meganium can use Sweet Scent to allure/distract Aizen with a pleasant aroma, likely making him easier to hit with what offenses it has.
Meganium, in battle, releases an aroma that soothes & becalms emotions. In battle, like here, it releases more to blunt the foe's fighting spirit, which could possibly make Aizen have more trouble fighting back.
Even while hypnotized, if Meganium can control what it does, it can attack everything around it with Petal Blizzard, or use a homing attack via Magical Leaf, the leaves of which themselves chase the target, apparently. This provides Meganium semi-reliable means of attacking Aizen even at range or under the effects of Kyōka Suigetsu.
Aizen's biggest advantages are making Meganium's senses worthless, so that it's hard for it to detect him, & his pseudo-flight allowing him to keep mostly out of range & use his own ranged attacks. If his 7-B stats form also has Reality Warping &/or Regneration, this could also be useful.
If it can still control what it does, though, as mentioned, Meganium has ways of fighting, even if it can't see, hear, smell, feel or taste to detect them.
The fact that it can halve the damage of attacks, block statuses in several ways, heal & Poison Aizen means it could have an advantage in the long term.
I have my doubts about Kyōka Suigetsu
giving Aizen an easy win here. I don't know how his Reality Warping works, though, nor if he has it or his Regenerationn in this form.
I'll laugh if Aizen's profile ends up with a win against Groudon & a loss against MEGANIUM of all things. XD
Hopefully my points seem valid, & dare I do it, I vote: Meganium High Difficulty, for being able to attack everything around it, homing attacks, damage halving, healing, status blocking & curing, scent-based alluring/distracting/becalming/battle-spirit-blunting & via PoisonPowder... err... poisoning.
Without complete knowledge of Aizen's RW nor knowing if he has it &/or how good his Regenerationn is, in his 7-B stats form as the OP specified here, I'm not sure his hypnosis, pseudo-flight, range & stats are enough for him to win here, silly of me as that may be.