Celestial Bow

Unlock
To unlock the Celestial Bow, you must first find the recipe for it while doing the final PGC. To do this, you need to have the Portal From Beyond event occur within or after the boss room (room 30) in Depth 3 Mountain, while Archer is in the team. Havixx has a more in-depth guide for PGC 25 located here: Havixx's PGC Cheat Sheet

Info
The bow's main purpose is to speed up the final PGC, giving you the ability to deal more damage to Rykker P.Baal v25. With a decent blacksmith, this bow should take you 1-2 hours to craft and it counts as a Tier 4 weapon. This means any gems you embed will increase stats by Gem Level * 4, helping you meet the 2,000 Speed requirement for Archer to speed up this challenge.

Warning The bow, and any embedded gem, will be destroyed after you beat this challenge. Be sure to unequip the gem before you deal the last hit to Rykker.

There are many ways to get Archer to 2000 speed, including using high-level Wind Gems or using high quality T3 or T4 Wind gear. The following example uses minimal gems, especially on the bow since that can be risky.

To reach 2000 speed on Archer having just the Celestial Bow equipped (+52%) you need Archer's base speed to be 1316. You can boost this with a T3 SSS+20 wind accessory (+78%) and armor (+39%) each with a level 1 wind gem (+3% each) to reach a total of +175% and reduce Archer's base speed requirement to 728, a 100k growth Assassin Archer will reach this base 728 speed at a Dungeon level of 143. Higher level Wind gems will reduce that base speed requirement further. This can help you to avoid placing a high level Gem on the bow and accidentally losing it after the challenge is done. (Thank you for the math, Odin)

Example
108k growth, lv15 wind crystal