Attacking his head will cause very little damage, but it is the simplest way to beat him. Performing a paraloop as close to the tip of his tail as possible will kill him instantly. This is the only boss to have an instant-kill move.
Outside of NiGHTS, Gillwing made a cameo in Sonic Adventure and Sonic Adventure DX as a card in the NiGHTS pinball table from Casinopolis and in Sonic and All Stars Racing Transformed in the Dream Valley circuit. Gillwing also appeared in Sonic Pinball Party and in the Nightmare Zone DLC of Sonic Lost World as a boss.
Gillwing's battle happens in a weird garden like environment with giant flowers which are constantly opening and closing, mushrooms which keep growing and shrinking, rocks floating around and two red suns, in the center of the area, there's a blue star spinning, it's possible that the garden is located in space or perhaps in another planet, due the dark sky, floating rocks and the two red suns.
In Christmas NiGHTS into dreams, some flowers are replaced by Christmas decorations and presents and the red suns are replaced by purple nebulas, there are gems spinning around the center of the stage and after the fight, a giant christmas tree appears in the center.
Gillwing's battle is known for being the fastest battle in the NiGHTS series, all he does is fly in circle constantly, the player can easily defeat him in a fraction of seconds by going behind him and paralooping the end of his tail tail, which will give a 21 links and if that's done early in the battle, a 2.0 score as well, however the player must be careful because they may touch his tail when trying to do that, which will damage NiGHTS. 
A slower, but safer way to defeat Gillwing is by simply grabbing and tearing off his head constantly, his head will regenerate and replace a part of his tail, but Gillwing will start to shrink, once there's no more tail, Gillwing will not be able to regenerate and he will be defeated, however the player should not run into his mouth, otherwise, it will damage NiGHTS. 
A translated Japanese bio for Gillwing states:
"By Second Level standards, he’s got a huge, enormous body but he’s really just a big air-head. The moment he considers you an enemy, he’ll stop at nothing to chase you down. He possesses the ability to re-grow his head from his long tail."
- There's a specie of dragons in the How to Train your Dragon series called Whispering Death, that curiously resembles Gillwing in some bits, these dragons have a green round head with yellow lower jaws, a green serpent-like body and spikes spreaded through their tails, the similarities are most likely coincidences though.
- Despite the similarities being most likely coincidences, It's rather ironic how these dragons happen to have the word "Whispering" in their name, which is the opposite of Gillwing, who is a screaming dragon.
- Sometimes, such as in the video game Dragons: Rise of Berk, there's blue in the middle of the Whispering Deaths heads and their lower jaws have a brighter yellow, making them look even more similar to Gillwing.
- The star at the top of the Nightmaren tree-like formation in Gillwing's realm in NiGHTS into Dreams actually has use in Christmas NiGHTS into Dreams as after you defeat the "Christmas Gillwing" you are awarded the star that will eventually sit atop a very tree-trimmed Twin Seeds tower. This will win you the game in Christmas NiGHTS, but you do not recieve the star at the end of the battle in the original game.
- Gillwing is known for being a loud dragon tadpole, so it's possible that he is the representation of what Claris fears she will sound like in the auditions, Gillwing could also have a connection with Claris' father, since he is the boss of Spring Valley, a level stated to represent Claris' high admiration for her father.
- In the Archie Comics, Gillwing has no connection with Claris nor meaning, he simply appears to be a very vicious and powerful nightmaren who will be released from his cage by Wizeman in serious situations, which in the comic's case, it was because Elliot had freed NiGHTS, additionatly, Elliot is the one who fights him and Claris never meet him.
- His name comes from the fact he has wings where tadpole's gills are located.
- In some of the earliest concept arts of the game, there's what appears to be a squid like nightmaren who was most likely one of Gillwing's earliest designs, due to his similar color patterns and the fact he is next to an early version of Puffy. 
- The third level nightmaren Party, looks a bit like Gillwing design wise, though with more feminine characteristics and different colors, also just like Gillwing, their tails are their main weapon.
- Gillwing and Puffy are tied as the second level nightmarens who made the most appearances, with a total of eight.
- Christmas NiGHTS into dreams was the only time where Gillwing appeared in something without Puffy and Game Gag 1P Comic Sega-hen was the only time where Puffy appeared in something without Gillwing.
- He is one of the two second level nightmarens who can be defeated by a single attack, the other is Queen Bella.
- Gillwing's theme is called "The dragon gave a loud scream".