Complex sentence: Sonic and Tails were removed from the game and replaced by Knuckles and four other characters, including Mighty the Armadillo, who first appeared in the "SegaSonic the Hedgehog" arcade game (1993).
Split into simpler sentences: Sonic and Tails were removed from the game and replaced by Knuckles and four other characters. Among these was Mighty the Armadillo, who featured previously in "SegaSonic the Hedgehog" (1993).