Not that it matters for Riki personally, since monsters can only equip accessories. The only accessories available in the junk shop are Junk and BrokenBumpers, which are both useless, so this trip is mostly for Gen and T260.
And Lute and Mei-Ling... I guess.
This scenario is lookin' awfully familiar.
Right. After each battle with monsters (rather than human enemies like Swordsmen), monsters in your party are offered the chance to absorb monster abilities. In the Game Boy games that started the SaGa series proper, this was explicitly by feeding on their delicious nutrient-filled flesh.
There are multiple abilities each monster can give you. Some are okay. Earlygame ones tend to be crap, of course.
And when a monster downloads abilities, it might change form.
The bottom slot of a monster's ability list is the one that new abilities go into. Here's the thing I didn't know when I played this game back when it was new:
you can rearrange those abilities out of the bottom slot to keep them. This makes monsters slightly more useful than I thought they were back when I was playing this on an actual Playstation -- but not much.
When a monster absorbs an ability, the game checks the abilities the monster knows against some predetermined lists, using a complicated system I barely understand where each ability is assigned a body part (Fang is a head attack, HeatSmash is an arm attack, Tail is a leg attack since there isn't a tail slot, and so on). If the first ability for each body part matches one of the predetermined lists, the monster changes form based on its HP.
For example, "DeathSynthesis" is the passive ability undead use to regenerate HP. It's on the transform lists for lots of undead monsters. So if a monster has Deathsynthesis on its ability list, the game will check against its HP to see what it turns into. Low HP equals a skeleton, higher HP a ghost, early-midgame HP nets you a zombie, and so on. If it has DeathSynthesis and one of Scream, Siren, or Supersonic, it turns into a GhostRider -- assuming the game doesn't check Scream first and turn your monster into a Harpy instead.
I have a mechanics guide for this and I still don't really get it. It's that needlessly complex.
Each form comes with their own HP, LP, WP, JP, and stats. They are not necessarily better than the form you just left -- Riki's Lummox form has all 7s in his base stats. The Xeno he just turned into drops his physical stats into the 1-3 range. Only WP and JP are restored upon transforming; it is quite possible to transform from a shape that has a maximum 3 LP to one that has 10 LP, but they're not refilled; it's near death already.
Oh, and every ability you absorb, whether it's forgotten later or not, increases the monster's maximum HP by 4. That's the only way monsters "level up" -- they don't grow after battle at all, except by the chance that they absorb a new ability.