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Staff of the Scarlet Sands
Cyno's signature weapon and Best-in-Slot providing bountiful stat boosts, especially when using an EM sands as it double dips into Cyno's EM + ATK scaling.
Ballad of the Fjords
Second best option for Quickbloom, highly competitive for Aggravate teams. If you need to pick a Battle Pass weapon for Cyno, pick this.

White Tassel R5
Excellent low investment, F2P weapon choice for Cyno owing to the large, uncoditional NA DMG% and crit rate mainstat it has — even with its notably low base attack.

Kitain Cross Spear
Consider in Quickbloom teams. Good craftable option.

Primordial Jade Winged Spear
One of the few times PJWS' passive stacks can be utilized to the fullest extent, showing its potential on sustained On-Field characters.

Deathmatch
Strong 4 star weapon that provides a large amount of Crit Rate for Cyno to better balance his Crit ratio, but is not worth purchasing a copy of/ refining for should players have an R5 White Tassel.

Staff of Homa
Although better than his F2P weapons and marginally better than a low-refinement Deathmatch, it is far more recommendable to use homa on other characters that benefits more significantly in comparison to Cyno. ( With the exception of aesthetics )

Missive Windspear R5
Event weapon that — although viable — does not perform better than the already impressive and mostly uncontested White Tassel R5. Only consider upgrading if the player had foddered their White Tassel.

<sands> Elemental Mastery or ATK %
<goblet> Electro DMG Bonus
<circlet> CRIT Rate or CRIT DMG

Energy Recharge ( check notes for ER requirements )
CRIT Rate
CRIT DMG
Elemental Mastery
ATK %

1) Elemental Burst: Sacred Rite: Wolf's Swiftness
2) Elemental Skill: Secret Rite: Chasmic Soulfarer
Normal Attack: Invoker's Spear should remain unlevelled as his Electro-infused Normal and Charged attacks during his Burst status scale based off of his Burst talent — not his AA, but are still treated as NA/CA/PA damage.

EM vs ATK?
Overall, they have similar performance with a few exceptions; use the one with better substats. Generally, low base attacks prefer EM sands while high base attack weapons would prefer ATK sands.

ER Requirements?
Solo Electro ~ 160-180%+
Double Electro ( Fischl ) ~ 100-120%
Double Electro ( non-Fischl ) ~ 120-150%
*ER requirements assume 1 favonius proc; 4 TF lowers ER requirements further*

Regarding 4 Thundering Fury…
Works well for Cyno — both to lower ER requirements and increase personal damage — but restricts users to a fixed combo as the reduction in E CD can be more detrimental than helpful. ( owing to missing Endseer timings )
For most, it is more recommended to ditch 4 Thundering Fury on Cyno unless confident in executing the specific combos.

Marechaussee Hunter
Only with Furina, a quickbloom team with this set is viable.