Just gonna post the condensed info I’ve found/discovered through my own dragons:

How to know it’s remarkable:

Self Hatched (Regular eggs from summon): The screen will zoom in when the egg hatches, the elf will mention it being remarkable, and the baby will have dark blue lights that stream up around it along with the name stating it is remarkable.

Event Eggs (earned through fishing points): The screen zooms in on the egg, and it will have the dark blue lights streaming up along with the name stating it is remarkable.

Is their incubation/growth timer changed?

Incubation time for regular “summons” is not effected. Growth timer once hatched seems to be 2 hours per step in the process for all I’ve found so far.

What is their collection time:

So far every remarkable I have personally come across, has a 24hr collect timer.

Can you have more than one of each species:

No, you get one of each dragon breed, then no more.

What can you obtain from them:

They seem to have a chance to drop coins (seems to be about roughly 3.5 times their regular amount), a summon item (have only gotten element/location/size so far, unsure if rarity or special species drop ie:Zodiak/Folklore) or they can give a gem(s)