Item 1: https://backpack.tf/item/10624700725

Sale 1:

https://backpack.tf/profiles/76561199085308746#!/compare/1767139200/1767225600

https://backpack.tf/profiles/76561198415225311#!/compare/1766534400/1767312000

11 keys

Item 2: https://backpack.tf/item/11967090875

Sale 2:

https://backpack.tf/profiles/76561199102199351#!/compare/1767398400/1767484800

https://backpack.tf/profiles/76561198087092525#!/compare/1767312000/1767744000

14 keys 21 ref, rounds to 14 keys

Sale 3:

https://backpack.tf/profiles/76561198087092525#!/compare/1772582400/1772668800

https://backpack.tf/profiles/76561199026390261#!/compare/1772496000/1772582400

Dumped to STN for ~12 keys

Sale 4:

https://backpack.tf/profiles/76561199026390261#!/compare/1772841600/1772928000

https://backpack.tf/profiles/76561198071230830#!/compare/1772841600/1772928000

14 keys

Item 3: https://backpack.tf/item/12138562784

Sale 5:

https://backpack.tf/profiles/76561199581722058#!/compare/1768867200/1768953600

https://backpack.tf/profiles/76561198034287318#!/compare/1768867200/1768953600

Untrace

Item 4: https://backpack.tf/item/3185190422

Sale 6:

https://backpack.tf/profiles/76561198111368575#!/compare/1771286400/1771804800

https://backpack.tf/profiles/76561198085861958#!/compare/1771718400/1771804800

Bulk for the Arcana Horrific Headsplitter

Sales:

11, 12, 14 (x2)

Sellers:

BPTF - https://imgur.com/tpYltr3 21 keys (2 month)

MPTF - https://marketplace.tf/items/tf2/1110;5;u3092 none

STN - https://stntrading.eu/item/tf2/Unusual+Mysterious+Mixture+Taunt%3A+Rock%2C+Paper%2C+Scissors none

SCM - https://steamcommunity.com/market/listings/440/Unusual%20Taunt%3A%20Rock%2C%20Paper%2C%20Scissors?filter=Mysterious+Mixture https://imgur.com/Ji2SdQq none

12 appears to have been a quicksell, however nothing indicates that 11 was low when it sold. Buyers are as low as 10 keys as of now and it's clear that 11-12 is as common of a trading point as 14 is.

Going with 11-14 keys