When you see the Jersey Devil at the old house in the forest, it flies away. Use the grappling hook from the attic to climb the tree next to the house.
Bring them back to the Mews lab for DNA testing.
You need a photo of the actual Nessie, a tooth from the chupacabra, and egg shells from the Jersey Devil. (see the related questions below)
You need a photo of Nessie at Loch Ness, a tooth from the Chupacabra from Puerto Rico, and egg shells from the nest of the Jersey Devil in New Jersey. (see related solution)
In a nest at the top of the tree at the old house in New Jersey. You need the grappling hook from the attic to reach it.
It's not the chicken eggs, it's the egg shells from New Jersey. When run through the DNA testing, the egg shells from the nest in New Jersey prove the existence of the Jersey Devil.
Take the shells back to the Mews lab and test them. The DNA analyzer will prove the existence of the Jersey Devil.
go to mew's mansion to continue your journey.
You will find a rope inside and you can get the egg shells from the nest of the Jersey Devil. Then you can prove it exists. You still need to get the photo from the Himalayas and also prove the Loch Ness Monster and the chupacabra. Once the three are proven, you will be sent to chase Bigfoot instead of the Yeti.
As you leave the attic of the old house, you see the Jersey Devil through the windows. As you go outside, it flies away. Climb the tree to recover broken shells from its eggs. You need the Grappling Hook from the attic (at the right behind the barrel with the raccoon).
You place one of the samples (fur or egg shells) in a vial and follow the instructions on the right side of the screen. When the x-ray grid is in the developer, push the flashing button.
During the DNA testing on Cryptids Island, you will add the sample (fur or egg shells) to a beaker, then before add an enzyme (the red #3). Before putting this mixture into the tray, you add Lab Gel, which is yellow in color, to the tray. When you add the orange sample beaker, the tray also turns orange.
You can find egg shells by exploring the island and searching in various locations such as on the ground, in nests, or inside creatures. You can also trade with other characters for egg shells or receive them as rewards for completing quests.