The concluding half of Jim Shooter’s 2-parter is not much better than the first. His final few Legion tales have lost the spark of his earlier stories. Adventure 379 (April 1969) is mediocre at best.
Ultra Boy and other Legionnaires return from a mission to find their dead friends, and time stopped by an odd alien, who convinces them to go to his realm of Seeris. The beings from that world have mental abilities, but frail forms, and are being over run by brutal invaders.
The best scene takes place between Ultra Boy and Phantom Girl, some sincere elements of their relationship, and Ultra Boy agonizing over his responsibilities as leader, which none of the previous ones were ever shown to do.
Chemical King also gets a good bit, using his powers on himself, to increase his metabolism, briefly endowing himself with super-strength.
The Legion convince the aliens to use their mental powers to defend themselves (sad they had to be convinced), and that turns the tide.
They return home, and Ultra Boy uses the Miracle Machine to restore the dead-ish Legionnaires to life. The biggest disappointment in the issue is that the killer is a nothing character, a person who never appeared before, or since.