The Jersey Devil can be found near an old deserted house (address 666) in the forest at New Jersey. In order to get to the house, you will need
Open the locked dumpster with the bolt cutters, and take the junk door into the restroom. Matching it to the other door gives you driving directions through the woods. Before you leave on the motorcycle, USE the matches and the lantern will be lit. Follow the directions (or just steer right left, right left, right left) and you will reach a dead end in the forest. Use the "look around" to get off the bike and enter the gate. Inside the house, go to the second floor and push the dresser left to reach the attic. The noise is just a raccoon, but get the grappling hook and go back downstairs. You will encounter the Jersey Devil!
Go outside and climb the tree with the grappling hook. Take some egg shells back to the Mews lab, and do the DNA test to confirm the existence of the Jersey Devil.
Yes, you can find proof of The Jersey Devil, Bigfoot, Nessie, and the Chupacabra. (see related question)
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)
To win the island, you must find the proof that confirms the existence of three legendary cryptids : Nessie of Loch Ness, the Chupacabra, and the Jersey Devil. Then you have to rescue the 4th creature, Bigfoot, from the evil plans of Gretchen Grimlock. (see related solution question)
The proof for Nessie is a photo from Loch Ness. The proof for the chupacabra is a tooth from Puerto Rico. The proof for the Jersey Devil are egg shells from its nest in New Jersey. You cannot prove the Yeti, but when you have proven the other three, you go to follow Bigfoot, which is a similar creature. (see the related questions)
The grappling hook is part of the solution in New Jersey. It is in the attic next to where the raccoon appears. Use the grappling hook to climb the tree and recover some egg shells from its nest. Take this back to Mews, as it provides proof of the Jersey Devil.
You don't. Gte the lantern from the monastery, and take a photo of the footprint in the snow. But Mews is not convinced so you don't go back. Instead, once you have proved the other three cryptids (Nessie, chupacabra, and Jersey Devil), he sends you to hunt Bigfoot, who is similar to the Yeti.
You don't find a photo, you take a photo, on the trail above the monastery in the Himalayas. You also collect the lantern there. But back at the Mews lab, the footprint is not convincing proof. You don't have to go back to the Himalayas. Get the proof for the other three cryptids (Nessie, chupacabra, and the Jersey Devil) and an opportunity to get the Yeti/Bigfoot will present itself.
Since the monks won't let you test the Yeti scalp, you have no proof. Once you have the lantern and the footprint photo, you can find nothing at the Himalayas. However, once you prove the other three cryptids (Nessie, Chupacabra, and the Jersey Devil), Mews will send you in pursuit of the similar creature, Bigfoot.
You don't actually confirm the Yeti. You just need to get the photo of the footprint, which is not enough proof. When you have proven the existence of the other three cryptids (Nessie, Chupacabra and the Jersey Devil), Mews will send you in pursuit of the similar creature, the Bigfoot, in the Pacific Northwest. Bigfoot is obviously confirmed at the end of the trip there.
He only sends you after you have proven Nessie (photo), the chupacabra (tooth), and the Jersey Devil (egg shells). You also have to get a photo of the snow footprint from above the monastery in the Himalayas, even though it is not convincing proof.
Since you can complete three of the cryptids in any order, that would depend on what you have already done. But you don't have to go back to the Himalayas once you have the lantern and the footprint photo. Get the proof for the other three cryptids (Nessie, chupacabra, and the Jersey Devil) and an opportunity to get the Yeti/Bigfoot will present itself. (see related question)
You don't. After you get the lantern and the footprint photo, there is no other proof available in the Himalayas. Once you prove the other three (Nessie, Chupacabra, and Jersey Devil), an opportunity will come up to chase Bigfoot instead of the Yeti, since they are similar creatures.