Name: Woobat
Availability: Early. Very commonly encountered in the Relic Passage.
Stats: Woobat's only great stat is Speed. Base 114 Speed as a Swoobat ensures that you'll always go first so it works ok for sweeping routes. Aside from an average base 77 Special Attack, Swoobat's other stats are awful.
Typing: Psychic/Flying is a decent offensive type, Steel-types aside. Defensively, its strong match-ups against Ground and Fighting are nice, but 5 weaknesses is a lot for such a frail Pokemon.
Movepool: Woobat starts with STAB Gust and Heart Stamp, and Air Cutter comes at level 21. Air Slash (level 32) and Psychic (level 41) are the late game replacements. Shadow Ball from TM provides coverage, and if you hoard shards you can get some nice moves from the move tutors, with Heat Wave being particularly helpful for coverage against Steels. If anything, Swoobat learns Fly so it can provide utility at least.
Major Battles: Woobat works well against Burgh but hates Dwebble. It doesn't really work that well anywhere else. It may seem like it would work well against Marshall, but most of his Pokemon have Rock moves that destroy Swoobat, and they can survive a hit.
Additional Comments: Woobat evolves by happiness, so you're going to have to work hard to keep the frail Woobat alive to prevent it from hating you.
Name: Cubchoo
Availability: Found on Route 7. Note that Cubchoo is only found in Winter (April, August, December), and if you are unwilling to change the month on your console then you may not be able to obtain it right away.
Stats: Before it evolves, Cubchoo is frail and slow, although its offenses are decent. It becomes much bulkier as a Beartic. Base 110 attack is very good but base 50 Speed isn't good late-game.
Typing: Ice is a great offensive type. Super-effective coverage on Dragon-types is rare and Beartic can provide that. On the other hand, Ice is one of the worst defensive types because it only resists itself and it's weak to Fire, Rock, Fighting, and Steel.
Movepool: Decent. Its movepool isn't that good before evolving, but it learns Icicle Crash right after evolving, guaranteeing it access to a powerful physical STAB. Superpower can be relearned by Beartic with a Heart Scale, as can Aqua Jet. It gets goodies like Dig, Shadow Claw, and Rock Slide from TMs.
Major Battles: Beartic is decent against Skyla's gym, although only 1 of Skyla's Pokemon is actually weak to Ice. It's very good against Drayden and it should be able to survive at least one super-effective hit. It isn't that helpful against Marshall, but the other Elite 4 members carry at least 1 Pokemon weak to Icicle Crash (Drifblim, Golurk, Krookodile, Sigilyph), and it can work well against Iris's Dragons.
Name: Dwebble
Availability: Found in the Desert Resort; it has a 10% encounter rate.
Stats: The Dwebble line focuses on Defense, although Dwebble's Attack is decent too. When it evolves, it can take Special attacks pretty well. Dwebble's main problem is its Speed, which actually drops after it evolves.
Typing: Bug/Rock is a neat offensive type that covers 6 types super-effectively. Steel-types wall it but these can be covered by other moves. Defensively it's a bit disappointing, with only 2 resistances (Normal and Poison).
Movepool: Dwebble starts with Smack Down and gets Bug Bite soon after. Rock Slide at level 29 is excellent, and it learns X-Scissor later on too. It can learn Dig, so Dwebble can achieve fantastic coverage right from the start. Crustle also gets Shell Smash for sweeping. Shell Smash also helps make up for Crustle's poor Speed, although it'll still be rather slow after 1 boost.
Major Battles: Dwebble can contribute against Elesa and Clay but a full sweep is unlikely. Its late-game match-ups depend on how well it can set up against the lead. Skyla's Swoobat and Grimsley's Liepard should be easy set bait assuming you don't get hit by Attract. A few Full Heals should help you set up against Caitlin's Musharna too.
Additional Comments: Both of Dwebble's abilities are good. Sturdy probably has the edge because it helps set up Shell Smash more easily.
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I'm not reserving any more of these for now, but I'm going to do a run-through of White 2, using Venipede, Rattata, Basculin, Zebstrika, and Drifblim. The 6th slot will be Tepig initially but I might change that later. I'll post my thoughts when I'm done.