Monster Combat level Quantity Rarity Zulrah 725 1 Very rare (1/6,553.6)
The drop rate for this item is calculated from two different rolls: The chance of rolling Zulrah's flax table (1/25.6) and the chance of rolling the mutagen table (1/256).
Thus, multiplying these two fractions will result in 1/6,553.6, which is Zulrah's chance of dropping a mutagen, or a 1/13,107.2 chance of a specific mutagen.
However, since Zulrah gives two rolls to its drop table per kill, the chances are doubled, giving a 1/3,276.8 chance for any mutagen or a 1/6,553.6 chance for a specific mutagen.
- Jagex. Mod Ash's Twitter account. 10 May 2015. Mod Ash: "Yes. The flax bit is 10/256, so each mutagen is therefore 1 in 13.1k. or 1 in 6.5k of getting either colour."
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