I recommend that you make your Lead Gligar a defensive Pokemon, which means you have to switch everything around. Here is what I recommend:
Impish Nature(-Sp. Attack +Defense)
EVs-252 HP, 188 Defense, 34 Attack, 34 Sp. Defense
- Stealth Rock
Here you go. Stealth Rock sets up entry hazards, Taunt sops other leads that try to setup on you. Earthquake is obvious STAB while Roost restores HP. Since you are using Taunt, you might want to get some Speed EVs so you can actually use it.
All I can say is to switch the Nature to Adamant for that extra power. Otherwise, no suggestions.
I suggest replacing it with Accelgor, since it cannot sweep or Outspeed. Here is a set for it:
- Giga Drain
- Bug Buzz
- Focus Blast/Hidden Power Fighting
- Acid Spray
Give it an Modest Nature with Sweeping EVs. It doesn't need a Timid Nature because 140 base Speed is high enough for a Modest Nature.
You are right about Cryogonal being frail. Replace Round(why?)with Rapid Spin to spin away Hazards.
I suggest replacing it with Dragonair as a Special wall, and you still keep a Dragon as well.
Careful Nature(-Sp. Attack +Sp. Defense)
EVs-252 Sp. Defense, 252 HP, 4 Attack
- Toxic/Thunder Wave
- Aqua Jet
- Dragon Tail/Outrage
I hope that works.
This thing is a TOTAL mess! Here is a new Meganium:
Calm Nature(-Attack +Sp. Defense)
EVs-252 HP, 128 Sp. Defense, 96 Defense, 32 Sp. Attack
- Leech Seed
- Energy Ball
Standard Sub-Seed. Good luck with your team