My impressions:
Galvantula: Frail, but hits hard. Good avaliability appearing just before Flying-Gym to kill Tranquills and Swannas.
Compoundeyes is a great ability but Thunder misses on the worst situations.
Speaking of TM Thunder, it has a good avaliability.
Mid/High Tier. High if it could learn Bug Buzz not as late as it can learn it.
With 7 level less or the like, Catlin's Musharna was a 3KO with Signal Beam.
Musharna: I envolved mine after learning Moonlight. Very useful at this point with Yawn/Hypnosis/Psybeam/Moonlight but its usefulness decreases through the game. I didn't use it against N and Ghetsis.
Mid tier.
Samurott: Useful, good but not great defenses and attack. Shell Blade at 17 is good and could go mixed with Surf and Shell Blade.
Also Megahorn is very useful, and Aqua Jet with priority. Torrent as ability is also good being mid-fast and Aqua Jet.
High tier.
Simisage: Useless until it learns Flame Burst, I envolved mine after that. Acrobatics is great ingame(I learned her with TM) for things that resist Fire, there are few useful items for ingame(Amulet Coin and Lucky Egg) avalaible at that point.
Very useful, also learns Yawn, for dangerous situations(letting it die and revenge kill with another) and Work Up, but frail to use 2 at the same time.
Mid tier. Maybe Mid/High
Lilligrant: Too good. Sleep Powder+Quiver Dance+Giga Drain and Own Tempo for avoid that annoying Confuse Ray and Swagger and for the future Petal Dance. Chrollophyll is almost useless, almost there is not Sun and +1 Quiver Dance is enough.
The only thing you have to do is to obtain Solar Stone at Nimbasa. To learn Giga Drain is not required, but recomendatted, you can go with Magical Leaf.
Sap Sippers and 1/4 Grass resistors are too rare.
She could sweep the Ghost-E4 entire team, It is true that Cofragigus is a setup fodder, but I wanted to test if Petal Dance activated Mummy, it does.
High tier.
Sawk: He solo'd Dark-E4 with Bulk Up+Rest+Revenge. I had hax because it never missed Revenge with 2 Sand Attack from his Scrafty
His slowliness could be annoying, but is very useful.
Mid/High tier.
Watchog: Not as bad as it looks, but not so good, but I didn't tested mine much.
Useful for catching pokemon, with Super Fang and Hypnosis.
Mid Tier.
Galvantula: Frail, but hits hard. Good avaliability appearing just before Flying-Gym to kill Tranquills and Swannas.
Compoundeyes is a great ability but Thunder misses on the worst situations.
Speaking of TM Thunder, it has a good avaliability.
Mid/High Tier. High if it could learn Bug Buzz not as late as it can learn it.
With 7 level less or the like, Catlin's Musharna was a 3KO with Signal Beam.
Musharna: I envolved mine after learning Moonlight. Very useful at this point with Yawn/Hypnosis/Psybeam/Moonlight but its usefulness decreases through the game. I didn't use it against N and Ghetsis.
Mid tier.
Samurott: Useful, good but not great defenses and attack. Shell Blade at 17 is good and could go mixed with Surf and Shell Blade.
Also Megahorn is very useful, and Aqua Jet with priority. Torrent as ability is also good being mid-fast and Aqua Jet.
High tier.
Simisage: Useless until it learns Flame Burst, I envolved mine after that. Acrobatics is great ingame(I learned her with TM) for things that resist Fire, there are few useful items for ingame(Amulet Coin and Lucky Egg) avalaible at that point.
Very useful, also learns Yawn, for dangerous situations(letting it die and revenge kill with another) and Work Up, but frail to use 2 at the same time.
Mid tier. Maybe Mid/High
Lilligrant: Too good. Sleep Powder+Quiver Dance+Giga Drain and Own Tempo for avoid that annoying Confuse Ray and Swagger and for the future Petal Dance. Chrollophyll is almost useless, almost there is not Sun and +1 Quiver Dance is enough.
The only thing you have to do is to obtain Solar Stone at Nimbasa. To learn Giga Drain is not required, but recomendatted, you can go with Magical Leaf.
Sap Sippers and 1/4 Grass resistors are too rare.
She could sweep the Ghost-E4 entire team, It is true that Cofragigus is a setup fodder, but I wanted to test if Petal Dance activated Mummy, it does.
High tier.
Sawk: He solo'd Dark-E4 with Bulk Up+Rest+Revenge. I had hax because it never missed Revenge with 2 Sand Attack from his Scrafty
His slowliness could be annoying, but is very useful.
Mid/High tier.
Watchog: Not as bad as it looks, but not so good, but I didn't tested mine much.
Useful for catching pokemon, with Super Fang and Hypnosis.
Mid Tier.