The Ether Mine is equally as large as, if not larger than, the Colony 9 region- and really is a region to itself, containing multiple areas each with more than one floor. Accordingly, it’s Collectapaedia page is the largest you’ve seen yet.
Ether Mine Collectables
Animals: Light Bat, Black Frog, Yellow Cat
Reward: Back Atk Plus II Ether Gem
Bugs: Black Beetle, Rubber Mantis, Mystery Firefly
Reward: Bleed Defence III Ether Gem
Nature: Charcoal Leg, Ether Pebble, Rumble Coal
Reward: Recovery Up II Ether Gem
Parts: Black Chip, Ready Coil
Reward: Topple Up II Ether Gem
Strange Things: Love Crane, Fire Abron
Reward: Muscle Up II Ether Gem
Page Reward: Rayon Pike (2 slots)
Even if you do lurk in the initial tunnels for some time and finish up by going to Moss Lake, don’t expect to complete the whole page before moving on to the larger caverns of the mine. Don’t worry about it either- while the Ether Gems are nice, the most powerful one (Bleed Defence) covers something you’re not often worried about, and the Page Reward, while interesting, is not the best weapon to have for Reyn that you can get right now. Most of the rewards here are specialized, only the Muscle Up gem being worth a lot of interest, though a case could be made for Shulk wanting that Back Atk Plus gem rather badly.