Unbeatable moveset

I was battling in Battle Factory, getting pretty far. This trainer threw out a Meganium at me, i didnt thnk anything of it. I got it down to a sliver of health and everything went wrong. This is what it was.

Meganium. Level 100. holding Leftovers

Double Team
Leech Seed
Grasswhistle
Substitute

It had no move to cause direct damage to me. It maxed out its evasiveness with double team. Leech seeded me so i lost health slowly. Substituted so i wouldnt do damage, and while it was substituted leech seed and leftovers would heal it. There was no way to defeat this Meganium.

Kind of annoying thing in the factory. However, there are many ways to kill it. Fast pkmn with substitute can easily switch it off. Another effective method is to roar/whirlwind it away... Or haze. Or 100% accuracy attcks (aerial ace!!). Or pkmn with liquid ooze ability. There also are many other ways... But there's no such thing as unbeatable moveset, trust me. Even without correct moves/abilities it is possible to beat that thing. Make sure to choose good pkmn at the factory!

I'd use Giga Drain instead of Double Team though, just because of competitive rules.

i think id take double team still so there is no way of hitting him

if i were to make a meganium with this moveset, what evs should i give him?

yes i had aerial ace and such. but whenever i would use it, i was either asleep, or he had a substitute.

ANYBODY KNOW WHAT EVS TO GIVE HIM???? WOULD IT BE DEF, SP.DEF, SPEED?

i remember my team now. it was
Dugtrio
Aggron
Hariyama
All lvl 100

I don't know about the evs. I would max out hp and give a bit more to sp.def than def. This is like a tank so I wouldn't give any speed at all.