Light Metal
The user's weight is halved and their Speed is doubled, but their Attack and Defense are decreased by 33% each.
Why: Lighter=more maneuverable, but it probably also means less strength of armor and less weight behind physical impacts. I mean, I suppose Game Freak might've been going for a different kind of metal that's lighter but just as strong, but I've never had any reason to suspect it beyond the framing of the name, which is still pretty ambiguous.
Incidentally, this would probably be Mega Metagross' preferred base Ability unless it was concerned about Sticky Web more.
Heavy Metal
The user's weight is doubled and their Attack and Defense are increased by 50% each, but their Speed is halved.
Why: The inverse of Light Metal.
I think Aggron would genuinely have a hard time selecting between this, Sturdy, and Rock Head, while Bronzong might finally run something other than Levitate -particularly Trick Room variants.
Liquid Ooze
When an enemy steals health from the user, they lose the amount of health they would have gained instead. Additionally, the user
Ok yeah I got nothing