Gigapede is a boss encountered at the end of Mission 4. Two others infest Leviathan's intestines, but these are not boss encounters.
This boss in Mission 18 is optional and Dante can skip this boss with the Gigazip trick.
Vergil will have to abuse PS during Beo / FE SC while Dante uses only SC between Reb / Cerb.
Standard Dante cycle.
Standard Vergil cycle.