Kenefactor
Terrarian
It was a mod that added different races (Not N Terraria). One race was a slime person that got abilities when they killed a slime type for the first time, e.g. Metroid-like morphball once they've killed Pinky, or being able to roll up walls in that morph-ball form once you kill a jungle slime. There also was some sort of cyborg or robot with glowing eyes and a glowing stone in torso of same color; they could use stacks of 20 of various ores to upgrade a built-in Megaman-style arm cannon they had. This mod may have been part of some bigger mod, possibly one with RPG leveling mechanics. I know it was for an early enough version of Terraria that slopes didn't exist yet. I'd greatly appreciate any information people have to share.