Answers to last week's trivia. I think this might be my longest trivia answer post.
1. Other than Superboy or Supergirl, which Legionnaire(s) has/have traveled to an alternate timeline or parallel Earth from their own "mainstream" universe? And who was the first Legionnaire shown to meet his/her alternate-universe double?
The first was Chameleon Boy, shown (with Proty) meeting his alternate-world double.
I'm not quite sure how to reconcile certain Legions with any particular Earths, but here's my best shot:
* Pre-Crisis Earth-1 / Pre-Crisis Legion
* Original Post-Crisis Earth / Post-Crisis Legion
* Unknown / v4/TMK Legion
* Post-Zero Hour Earth / Post-Zero Hour Reboot Legion
* Unknown / v5 Legion
* Post-52 New Earth / New Post-Crisis Legion
Others shown on alternate or parallel Earths (thanks to Erik for remembering some I had forgotten):
Pre-Crisis Earth-1 Karate Kid, visiting Kamandi Various Legionnaires visited Earth-2 during the Crisis (and probably other worlds too) Original Post-Crisis Legion Blok, Sun Boy, Brainiac 5, and Invisible Kid, visiting the post-Crisis Superman's Earth New Post-Crisis Legion Star Boy, visiting Earth-22 (Kingdom Come) in the early 21st century Post-Zero Hour Reboot Legion Shikari, visiting the v5 Legion's Earth Whoever visited the Pocket Universe Earth v4/TMK-era Phantom Girl swapped places with an Original Post-Crisis 20th century Durlan v4/TMK-era Valor and Timber Wolf in the Original Post-Crisis 20th century v4/TMK-era Ultra Boy getting zapped to ancient Egypt in the Original Post-Crisis timeline
Jim mentioned Ultra Boy and the Earth-3 Legion coming to the pre-Crisis Earth, actually it was Superboy who travelled to their Earth (remember, he went to the 20th century "Smallvile"). The Booster Gold crossover was from the Post-Crisis Legion to Post-Crisis Earth, so that was the same Earth (at the time). In retrospect I don't know if the Cosmic Boy/Night Girl trip works, since it was the Post-Crisis Legionnaires visiting the Post-Crisis 20th century, even though the Post-Crisis Rokk had memories of the Pre-Crisis 20th century (or something like that). The "Team 20" group came from the Post-Zero Hour 30th century to the Post-Zero Hour 20th century so I don't count that. And the Legion/Titans Univers Ablaze never happened.
2. Name three Legion-related characters who could use their senses to discern alternate realities (not other dimensions)?
Andrew Nolan and the Time Trapper were two easy ones. I don't remember Dream Girl, Sensor Girl, or the Infinite Man reaching into alternate universes, but I could be wrong, though Dreamer (of the Post-ZH Legion) could, as seen in L3W. And I specifically excluded other dimensions so that nobody would say Phantom Girl being able to see into the Phantom Zone and Bgztl, but Tom said it anyway. The one that nobody got was Antennae Lad – remember, in his first appearance, he heard a radio broadcast of JFK's re-election.
3. During the Crisis on Infinite Earths, who said (in effect) "But there is no Earth-2 Legion!"
4. The Earth-22 Legion was was based (at least visually) on the post-Zero Hour version. But who was a member of the Earth-22 Legion and not the post-ZH Legion?
The official list of Kingdom Come (now known as Earth-22) Legionnaires was given in the Kingdom Come slipcover edition, and are listed in the Legion Wiki (though it's missing the clearly-visible Catspaw). Last week's JSA #22 has a new half-page shot of the Earth-22 Legion.
The Legionnaires in the Earth-22 Legion and not the Post-Zero Hour Legion are: Bouncing Boy, Catspaw, Chemical King, Dragonmage, Inferno (Dirk Morgna), Matter-Eater Lad, Princess Projectra, and Supergirl (Matrix). Note that most of these did exist in the Post-ZH timeline but were not Legionnaires.
Duke, you may want to check out the panel from Kingdom Come, your memory is faulty with regards to some of the characters you think you remember.
5. What other DC character had a regular strip set in an alternate 30th century that did not have a Legion?
That would be Superman 2965, who had several adventures in the pages of Superman, Action, and World's Finest. This Superman's secret identity was Klar Ken T5477. Not coincidentally, Waid and Kitson wrote him into LSH v5 #16, as recounted here a few years ago, though never shown with powers.
Kamandi wasn't set in the 30th century, and Green Lantern as Pol Manning took place in the 58th century. Flash (Barry Allen) went to the 30th century but never had any kind of strip from his time there.
6. What do Star Boy and Mon-El have in common that no other Legionnaires have?
The answer I was looking for was that they were both based off of "twice told tales", Superboy or Superman stories rewritten with some details changed. The precursor stories for each were published in 1953. Lana tried to make Superboy jealous with Mars Boy (Adventure #195), while Superman met his big brother Halk Kar (Superman #180).
7. Which of the Legion villains that Superboy-Prime gathered in "Legion of Three Worlds" had never met the Legion prior to that story?
The adult Saturn Queen traveled back in time with Cosmic King and Lightning Lord, but the teenage version never appeared. (Note that in the v4-era, Eve Aries married Tenzil Kem, though I don't think there was any evidence one way or the other whether this was before she went back or afterwards. having reformed). The Legionnaire-age Cosmic King first appeared in the v3 LSV War story.
Also, Echo and Beauty Blaze appeared only in the Adult Legion alternate timeline story, though Echo was later shown to have joined during the Five Year Gap.