I understand how the hatchlings work: If you control Viserion, attach White Hatchling and all of its duplicates to Viserion as duplicates. Question is, if I have the misfortune of playing the hatchlings first, then do their adult counterparts come in to play as dupes of the hatchlings?

Nope - it's the other way around.

Once you play Viserion, the Hatchling attaches to him as a duplicate.

K, thats what I was thinking, Opponent in last game made me doubt myself a little lol. Thanks…

Forgot to ask, assuming the white hatchling is played first. Would you then pay Viserion's gold cost and then attach the hatchling or would you put Viserion in to play as a "duplicate" only attaching the hatchling to it instead?

Sealtyk said:

So, they are two entirely separate unique cards with entirely different titles. Just like any other completely different unique cards, there is no rule preventing you from playing them together, or having both in play at the same time. Once you do have them in play at the same time, the requirements of the Hatchling's effect kick in and the Hatchling becomes a dupe on Viserion. But not before then.

So, because these are totally separate unique cards that have no link until they are both in play at the same time, if the Hatchling is in play, you have to pay for Viserion - then resolve the passive effect once he is in play. Similarly, if you have Viserion in play, you have to bring the While Hatchling out of Shadows - then resolve the passive effect once he is.

Thanks, wanted to make sure I was using it rite.