|<This article is a stub. Help by adding to it.> Mastered Ultra Instinct Kostas (usually just called Kostas) is a Greek YouTuber that focuses on Sonic games and .EXE genre games. His birthday is in June 28th.
Sonic.exe: Tower of Millenium
Kostas appears in the game, as an easter egg. After being talked to, he disappears.
If Diana is the one that finds him, he encourages her. If Metal Exetior is the one that finds him, Kostas asks why he's there. Metal Exetior replies that he thinks this is the right path, but Kostas tells him that it's a dead end and briefly encourages him. If Sark is the one that finds him, Kostas berates him on betraying Exetior and wanting the world for his own selfish desires.
Kostas is white with three yellow-tipped tufts on his forehead, and some of his upturned quills are yellow. He wears blue fingerless gloves with golden rings, and his shoes are grey with a golden stripe. He has blue eyes.
- He and Jaiz consider each other to be like brothers because they are close and their birthdays happen to be on the same day.
- His older designs consisted of a blue Super Sonic and a permanently-white Hyper Sonic with minimal differences.
- His favorite character is Exetior.