Stagnated rhymes with:
designated, decaffeinated, decontaminated, denominated, designated, emanated, exterminated, germinated, halogenated, hydrogenated, hyphenated, impersonated, indoctrinated, marinated, opinionated, pollinated, polychlorinated, predominated, reincarnated, rejuvenated, renominated, resonated, ruminated, subordinated
Stagnated sounds like:
stagehand, stagnant, stagnate, stichnoth, stigmata