Edit: Dev response thanks to WhiterValkyrie for asking! You just have to spend 2-3 days without coming back to the nest for this creature to appear.
If you stay out late enough a giant angry whale will menacingly start following you. I don’t recommend fighting unless you have at least 2 healing balms, some blast/impact capsules, and preferably if your duo attack damage is maxed.
I believe the whale has 3 stages in the fight:
First phase easy peazy just deal damage using duo blast then duo impact.
Second phase it’ll have either a red or green aura. The red is weak to only DUO blast while the green is weak to only DUO impact
And finally the third phase is when it starts charging up its laser attack. Plenty of time to prep your shields and wait for it to attack. Not worth trying to squeeze in one more hit, trust me. I believe it attacks in two successions so wait for that second attack. After the second laser it should be stunned and you’re good to continue the combo.
Now for actually getting some damage on this unit you’re going to want to hit it with a blast or impact capsule while it’s stunned. Charging up duo attacks takes too long in comparison to having one/both of you using a capsule attack. Good luck and remember to block!