From the same issue that brought you the Strangest Clock in the Universe, the Taroc Creature!
A wee bit of setup: a few issues back Lightning Lad had sacrificed his life to prevent Saturn Girl from sacrificing her life to keep someone from dying. I know, I know, sorry. It's much more clear in the comic book. Prophecy is involved, which always muddies the plot-waters. What's important is that Lightning Lad dies and, like, two pages later they're wondering if there might be some way to bring him back. In Adventure Comics No. 312 they really get to work on that problem and scour the galaxy for possible ways to sin against nature and take the very powers of God into their sweaty teenage hands - something they never seemed to get around to doing for Ferro Lad. Or Invisible Kid. Or 1/3 of Triplicate Girl, Sun Boy, Karate Kid or 1/2 of Duo Damsel. Man, the Legion really blew its altruism wad (so to speak) on this resurrection.
As a part of the whole "tamper with forces heretofore reserved to the Almighty because we miss our electricity-spewing friend" plan the Legion look up any and all references to resurrection in their Mechanical Librarian and then go on a gigantic cosmic scavenger hunt to round up all possible ways that they could create a blasphemous, soulless parody of their friend. Among the leads that are followed up on is the mysterious Taroc creature. Let's watch:
The Taroc is known for dying and then somehow coming back to life again and so Saturn Girl and Mon-el take a trip to their very yellow planet, in hopes of... uh... I'm actually not sure what they're hoping for. I mean, unless the things come back to life by means of a magical sprite who roams their planet dispensing miracles of rebirth. Possibly they hope to use advanced future science to infuse his corpse with Taroc genes? That would work, right? Anyway, it would work on Star Trek - you'd just have to run him through the transporter a few times afterward.
As far as alien monsters go, the Taroc creature's fairly boss. The 'fat pteranodon' body and snake head are solid creature fare and I appreciate how the ones that are at rest have adopted the vulture pose as their own. What reall sells me on these things, though, is the purple hands that they have at the ends of their wings. Since they're obviously useless while the Taroc is in flight, my imagination tells me that the creatures use these hands to play cards. In fact, Taroc society's basic unit is the bridge group, and the outcomes of trials are decided by playing a form of poker known as 'Bgtzl Hold 'em'.
Not sure what happened to Mon-el's face but it sure is creepy. Also: haven't there been Taroc creatures on every bit of high land pictured so far? why did he leave Saturn Girl on that peak? Is it because he has no eyes?
You know, I'm kind of sad that they didn't try this method of reviving Lightning Lad. Seeing a tiny red-haired dynamo burst out of their dead friend's back would have been just the thing to help the Legionnaires shake off the blues.
Even if I wasn't incredibly fond of the Taroc creature's hands and love for Eucre, its disgusting method of reproduction (plus the fact that it seems to be made of papier mache) rate a solid
Space Serpents! I can't remember (nor do I care to check) why the Legionnaires needed to go to the Great Interplanetary Post Office on their search for a way to turn their dead friend into a mockery of human form and feeling, but when they do they see that it's being attacked by "Space Serpents, able to live in space and to eat metal and stone! They must be from another universe!"
Great Jumping Suns indeed, Lightning Lass. I do have to say, though, that that's a pretty good guess. I mean, you took a pretty bare set of facts and extrapolated the fact that these generic dragony things were from another universe? Phew. I gotta say, you're a better guesser than me. I think that you're almost as good as Superboy:
Anyway, Space Serpents, being from space, have never encountered anything like Sun Boy before. Because space is cold and dark - there is no sunlight. Sunlight is on planets, not space. Space is cold and the sun is warm.
The completely generic dragon-monsters get driven off in a pretty hokey way, but there's still one left and it's in a room with some guys. Since flinging bolts of lightning around willy-nilly might hurt the guys an alternate plan is thought up:
The Space Serpent is fooled by Proty. Oh, god. these things are so boring. I can't even be scathing. They're just dragons that eat post offices ("They must be from a universe of rabid letter-writers, Sun Boy!") and they're dumb. Yawn and yawn.