The Centipede Demon boss is one of the optional bosses in Dark Souls. This demon is reached just before Lost Izalith, underneath Quelaag's Domain and the Demon Ruins.

Can you skip the centipede demon?

Strategy. The Centipede Demon is susceptible to both magic and lightning damage, but is immune to fire. It is possible to skip this boss by being Rank 2 or higher in the Chaos Servant covenant to open the shortcut to Lost Izalith.

Is the demon Firesage optional?

The Demon Firesage is an optional boss in Dark Souls, located in the Demon Ruins.