Here is the full list of all 10 ReLinked achievements.
Defeat the boss "Spirit of the North"
Defeat the boss "Ball Lightning"
Defeat the boss "Seeker"
Defeat the boss "Watcher"
Defeat the boss "Borschevik"
Defeat the boss "Bee's Nest"
Defeat the boss "Fox"
Defeat the boss "Phoenix"
Defeat the boss "Yin-Yang"
Defeat the boss "Segmented Snake"