do random shit
bandit, MUL-T, and engeeer gameing, you get just by playing the game, but here is a list
mercenary: commit not alive by touching a thingy that you can find in a portal after looping
artificer: buy her off the slave market (10$) that you can summon at a funny rock for 1 testicle
loader, and this one's hard, go to stage 4 Siren's Call, find eeg, shoot eeg, shoot total 6 eeg, giant robot chuckecheese basketball is demonically summoned, kill it (hard), get free red item + loader
(it's worth tho loader can annihilate anything)
pittbull: go to the black market, jump into the abyss, find a cave, go in the portal in it, complete mini teleporters for free items and do them all for funny dog character
rex: go to the back of your drop pod, get the fuel array, bring it (without falling below 50% health)
(use loader + command artifact + drizzle mode) to stage 4 Abyssal Depths, find the dead robot(it's high up) and give it the fuel array. you have unlock p o t t e d p l a n t
captain: beat the final boss