The Gloom Four

The Gloom Four is a group formed with 4 rogues, Taryck, Ursula, Hero. EXE, and Blux who are summoned by Izuku Midoriya (Deku/Imoku Usagi) to defeat and get the Warriors of Time out of the picture.

Warriors of Time

They first appeared in Warriors of Time and are antagonists and enemies of Hero Studios, Twinkle Sparkle, Allan Dark, Blue, and EnderCraft summoned by Izuku Midoriya (who uses his whistle) in each episode and chapter and they're being hostile to Kovu too. They're also associated with Meta Knight and Zen-Aku as their creations.

Randy Cunningham: 9th Grade Ninja

They reappeared again after Izuku Midoriya and Karly Hackerbeth turned Randy Cunningham (aka the Norrisville Ninja) evil and Izuku calls them by using his whistle. Their plan is to invade Norrisville High and assassinate its students. However, they were defeated by each different student: Ursula (Debbie Kang), Taryck (Howard Weinerman), Hero. EXE (Julian), and Blux (Theresa Fowler).

Trivia
 * The monster roars are different and are used by each member:
 * Taryck: Scythe Tubby
 * Ursula: White Scythe
 * Hero. EXE: Anomaly 358
 * Blux: Anomaly Alex
 * The Gloom Four are the only villains to not fight and be antagonistic against the main protagonist Randy Cunningham, who turned evil under the influence of Deku and Karly.
 * Their song is a reference to The Black Four from Kimba the White Lion.