I'm thinking klink (or maybe klang?). Gears spin without going anywhere, and they interlock their teeth when they spin, so the gears sink their teeth into each other, meaning they bite themselves. Klink actually generates energy to support its life this way, so that could be seen as "eating" to the klink. Each gear klink has has an X eye, as if it's injured, and its match would be the other gear. As for the ability thing, apparently plus and minus got altered in gen 5 to not exclusively charge with the other ability, so plus and minus are identical now, "clearly two" referring to its third ability, clear body, which is effectively its second ability due to plus and minus becoming the same (despite their representing opposite charges). Or it could just refer to klink's being a single pokémon while having two abilities. And of course, it has extra gears added to it as it evolves.
If it's not klink, can you please give me a table to flip? I think I might need one.
Klink is correct! You covered almost all the clues in your explanation, but I'll list out the meaning for each line for clarity's sake:
It met its match: Refers to each gear of the Klink having a certain predestined match with another gear, as per the Black and Alpha Saphire dex entries
its wounds won't heal: Refers to the bandage-like X-eyes.
it must bite itself, to make its meal: About the two gears interlocking with their teeth and spinning together to make the energy they need to live as per all the other dex entries
Those two it has, oppose in name: Klink's two non-hidden abilities, Plus and Minus, are named after opposite charges
the choice is false, they're exactly the same: Plus and Minus are completely interchangeable as of Gen 5, when Klink debuted.
It's exactly one: Klink is exactly one foot in height
it's clearly two: Klink is composed of two gears.
One will double: Klink's evolution Klang is exactly two feet in height
it'll add something new: Klink gains a new gear when it evolves.
It can move a lot, while staying where placed: Gears can spin around while staying in place
Should you trust it? Probably not, it's-: The rhyme scheme suggests the ending is something like 'rather two-faced', referring to how Klink literally has two different faces.
Good job octoboy! I'm looking forward to seeing your riddle!