Tagging for Clauncher and Caterpie. Will get the write-ups soon.
EDIT:
Clauncher [X]
Availability: Route 8, Ambrette Town, Cyllage City (Good Rod). You'll need to backtrack from Coumarine to get it.
Stats: As Clauncher, its stats are all between 44 (Speed) and 63 (Special Defense). Once it evolves, it at least hits a decent 120 Special Attack, so it's got that going for it, but 59 Speed holds it back.
Typing: Pure Water-type, it only has two weaknesses. Unfortunately, both of these are in back-to-back gyms (Ramos and Clemont), so you won't be using Clauncher against either of those guys.
Movepool: It gets Surf and Waterfall, but you're best off with a moveset of Water Pulse/Dark Pulse/Aura Sphere/Surf. Dragon Pulse hits nothing super-effectively until Drasna. Dark Pulse and Aura Sphere will require Heart Scales. Clawitzer also gets Ice Beam, which isn't available until the eighth gym but gives some coverage against Dragon- and Grass-types.
Major Battles: Clawitzer isn't very good at first, but in the late-game, it demolishes Olympia and Wulfric with Dark Pulse and Aura Sphere. It destroys Malva's entire team, while it can be useful against Wikstrom and Drasna with the right moves and Diantha's Aurorus and Gourgeist,
Additional Comments: Mega Launcher gives Dark Pulse and Aura Sphere 120 Base Power. Water Pulse hits 135 with Mega Launcher and STAB. Finally, do note that getting Clawitzer requires Flying back to Cyllage City to obtain, and as such, isn't very efficient.
EDIT AGAIN:
Caterpie
Availability: Santalune Forest (both), Route 2 (Y only), 10% in Santaluen Forest in X, 20% in Santalune Forest in Y, 11% on Route 2. Metapod can also be obtained in Santalune Forest at a 4% chance.
Stats: Flat-out awful until Butterfree. It has 45 HP and Speed as its highest stats as a Caterpie, and its highest stat as a Metapod is Defense at 55. Even after evolving into Butterfree, it still only has 80 Special Attack and Special Defense.
Typing: Bug/Flying isn't bad, but Grant's a Rock-type leader. Also, Team Flare uses a lot of Fire- and Poison-types.
Movepool: Butterfree has a grand total of five level-up attacking moves: Confusion, Gust, Psybeam, Silver Wind, and Bug Buzz. Not only that, all of the good special attacking TMs that it can get (Psychic, Shadow Ball, Energy Ball) are located right at the end of the game (Psychic in the Pokémon Village, Shadow Ball in Terminus Cave, and Energy Ball on Route 20.
Major Battles: Butterfree is bad against the first two gyms. It gets some redemption against Korrina and Ramos, being able to use Gust or Psybeam to damage and use Whirlwind to stop Korrina's team from racking up too many attack boosts with Power-Up Punch. It can wreck Olympia if you have Bug Buzz (though you need to watch for Sigilyph). Unfortunately, Team Flare uses a lot of Fire-types, which Butterfree can't hit super-effectively with anything it has.
Additional Comments: Butterfree has bad stats, a barren special movepool, and has some crippling weaknesses. Overall, it's not recommended in-game.[/B]