Thanks, and congrats on the three stamps!
There isn't that much to know about how to get the Chromatic Eldalodon to be honest... I don't really consider that to be one of the "secrets" so if you want, I could quickly explain x)
Viewing post in Can You Beat Chroma? jam comments
It isn't that different from what you did to get the Tortolodon at the start.
You prep as usual, with no delay on the encounter tool's timer, and you need to time the start of the battle to that timer.
The added difficulty just comes from having to keep the cursor on the fish while waiting for the timer to run out.
So yeah, if you want to see how it's done, Hap.dev did so in his video at 43:58 (the comment above yours)