For the first egg hatch tip...
2.1 Last Biters
There are two Legendary monsters in the game known as "Last Biters". These monsters are named this way as they are able to use the move "Last Bite"
Last bite: 50 seconds - Deal critical damage to one opponent and heal for 50% of damage dealt. (Must be last monster on the field in order to use)
optimally speaking you would acquire one of these two in your first egg. With the right strategy and knowledge of opponents monsters you can quickly turn a battle of 1 VS 10 around and end up to win it off a Last Biter alone.
The Two Last Biter monsters are:
If you are tired of reloading or simply want to continue to play the game just go with the first legendary you get. These two are just the best when it comes to beating online events as early as possible.
NOTE: do not take this lightly. please read the PVE Events section of the guide to consider whether you think its worth to keep trying for penguini or golrock. It will help you a lot in these PvE events which are a vital part of the game.
You said someone confirmed it? did they actually gotten one of these new monsters with new update? because I have retested it 100x I get the same pool of monsters and no legendary. if there way to reset it properly maybe I am doing it wrong...