The Webmaster Spider (アミダクモ, Amida Kumo, also known by the fan community as the Bosspider and the Chain Spider) is a large mechanical spider serving as the first boss of the Iris Stages in Rosenkreuzstilette.
Its primary attack is crawling down the four chains in the elevator. Before it descends to ground, metal rods from the chains will emerge randomly. These rods will alter the path in which the Webmaster Spider will descend upon. The Webmaster Spider will follow the nearest rods in its path. The player will need to carefully and quickly examine where the Webmaster Spider will go. Sometimes the Webmaster Spider will release miniature Webmaster Spiders that will scatter on the ground before descending from the chains. There are also traps in the elevator that shoots out spears from both sides of the room, which can be avoided by sliding (or dashing) under them. When it reaches the ground, it exposes the core on its abdomen, which is its weak spot, briefly before it climbs up the chains and repeats the process again. During Desperation Mode, the elevator will rapidly fall down, causing the spear cannons to move up and down. The Webmaster Spider will descend from the chains much quicker then before and will release much more mini-Webmaster Spiders before its descent.
- The Webmaster Spider is a large reference to Bospider from Mega Man X, which also shares its attack pattern and weakness to an ice-elemental weapon.
- The kanji in its name (アミ) is a pun on both the spider's web and the world wide web.
- The spider's weakness to Freudenstachel references the fact that spiders are susceptible to ice-based weapons.