We've noticed a few of the characters we've introduced from other series aren't as well known as we originally thought and some others could've been described better...so here's a list of links to all the people have appeared so far who aren't Black Clover or Emperor and Dragon originals. We'll start including the links to otherworldly characters in later chapters. Hope this helps! P.s. All of their stories are worth checking out if you haven't seen/read them.
Magnus' Associates-
Itachi Uchiha- https://naruto.fandom.com/wiki/Itachi_Uchiha
Soifon- https://bleach.fandom.com/wiki/Su%C3%AC-F%C4%93ng
Iori Sengoku- https://gamaran.fandom.com/wiki/Sengoku_Iori
Akame- https://akamegakill.fandom.com/wiki/Akame
Madara Uchiha- https://naruto.fandom.com/wiki/Madara_Uchiha
...........
Galileo's associates-
Irene Belserion- https://fairytail.fandom.com/wiki/Irene_Belserion
Tsuchigumo- https://nurarihyonnomago.fandom.com/wiki/Tsuchigumo
Yomi- https://yuyuhakusho.fandom.com/wiki/Yomi
Derieri- https://nanatsu-no-taizai.fandom.com/wiki/Derieri
Veldora- https://tensura.fandom.com/wiki/Veldora_Tempest
Ddraig- https://highschooldxd.fandom.com/wiki/Ddraig
Jinbe- https://onepiece.fandom.com/wiki/Jinbe
...........
Demon War enemies(Seven deadly sins' group- the 10 commandments)- https://nanatsu-no-taizai.fandom.com/wiki/Ten_Commandments
Chandler- https://nanatsu-no-taizai.fandom.com/wiki/Chandler
Cusack- https://nanatsu-no-taizai.fandom.com/wiki/Cusack#:~:text=Cusack%20is%20very%20confident%20in%20his%20abilities,%20requesting,loyalty%20to%20the%20Demon%20King%20's%20second%20son.
............
Joker City's Doflamingo Crew (One piece's Donquixote pirates)- https://onepiece.fandom.com/wiki/Donquixote_Pirates
.............
Diamond kingdom
Gilgamesh- https://villains.fandom.com/wiki/Gilgamesh_(Fate)#:~:text=Gilgamesh,%20also%20known%20as%20Archer,%20is%20the%20secondary,a%20minor%20antagonist%20in%20the%20Heaven's%20Feel%20route.
Sosuke Aizen- https://bleach.fandom.com/wiki/S%C5%8Dsuke_Aizen