Cyno build recommendations

Rotations:

Non-TF: EQ N3E N5E N5 N2E N5 N2E - 3 Endseer
EQ N3E N5E N5 N2E N5 N2E N5 N2E - 4 Endseer

4pc TF: EQ N2E N4E N4E N5E N4E N4E - 3 Endseer
EQ N2E N4E N4E N5E N4E N4E N5E - 4 Endseer Option 1
EQ N2E N4E N4E N5E N4E N4E N4E N4E - 4 Endseer Option 2

Cyno is a DPS character that uses his burst to change stance and deal electro damage. The damage dealt during this stance is normal attack damage so burst damage buffs will not affect him. On most teams with an electro battery, he will want 120–150% energy recharge.

Regarding Weapon Choices

Kitain Cross Spear
This weapon is especailly competitive with the options higher on the list if Cyno is not being run with an electro battery.

Regarding Artifact Sets

Thundering Fury (4)
In optimal conditions, this is Cyno's best artifact set. This set is an especially competitive option when Cyno is the only Electro character in the team, as the extra Elemental Skill casts help alleviate his energy issues. Do note that casting his skill off cooldown with this set might lead to missing Endseer stance windows and losing overall damage. It is highly recommended to use a shielder with Cyno with this set.

Gilded Dreams (4)
This artifact set is better than Gladiator's Finale on Staff of the Scarlet Sands and White Tassel.

Thundersoother (4)
If you can guarantee 100% uptime on this set, it performs better than Gladiator's Finale (4). However, satifying this condition is infeasible on most teams.

Regarding Main Stat Choices

Sands
Elemental Mastery versus Attack is heavily dependant on the weapon and team Cyno is in. It is recommended to test each and/or consult an optimizer.

Circlet
With Staff of the Scarlet Sands, Elemental Mastery may be used as the circlet mainstat.