Given how Kricketune is C tier, I see no reason not to nominate Garbodor for the same tier. EDIT: Upon review and some feedback, I say C- for Garbodor instead. That late evolution at 36 really really hurts.
Garbodor
Pros
- Incredible availibility, right from the start in fact, just search the Alleys.
- Acid Spray as Trubbish at level 12, an incredibly useful base 40 power move that lowers the enemy's Sp.def by two stages on hit.
- Mono poison typing means it completely blanks PULSE Tangrowth, and also lowers its significant bulk with Acid Spray.
- Access to Stockpile and Toxic, both regular and of the Spikes variety, means it can simply outlast certain things with healing items
- Helps significantly against both Florinia, Corey, and other various fights throughout the early to midgame, right up to about Kiki.
- Aftermath is a solid and useful ability, can be great for picking up a double KO in desperate situations.
Cons
- Mono poison typing means you're useless against certain leaders like Shade and Radomus.
- Lack of any relevant coverage sans TMs like Psychic, Thunderbolt. or even Focus Blast, of which we currently have access to none of.
- Even with Stockpile, lack of any consistent recovery aside from Swallow means it's all to easy to get worn down without a heavy supply of healing items, leading it to be a cash grabber.
- Other than Aftermath its other two abilities, Stench and Weak Armor, aren't great. Stench CAN be useful with its flinch chance, but Weak Armor is actively a downside.
- Relatively late Evolution of 36, leaving you with Trubbish for longer than you want.
- Falls off HARD after the midgame, becoming virtually useless. Poor thing.
Of note, all points I've made for Garbodor here can also apply to Swalot, so putting it in the same spot might be a good idea.
EDIT: Small set of pros and cons for Swalot that are different.
Pros
- Encore access, something Garbodor lacks.
- Semi early evolution of 26(!), meaning you'll have it before Shade.
- Destiny Bond via egg moves. Usually fat enough to take a hit, no sash required!
- Most pros that Garbodor has, Swalot does as well.
Cons
- When Liquid Ooze is your best ability, you're pretty bad off here.
- Slow as molasses. Base 55 isn't awful but it's a real drawback in a lot of cases.
- Every con that Garbodor has, Swalot has in some way.