Spinnerex has a unique gimmick where enemies tagged by Spinnerex explode on death and spread toxin damage.
Primed Pressure Point: +165% base damage. Condition Overload is an alternative option if you are using a primer (either manually via epitaph/nukor or passively via companions like Diriga or hounds) since it has a higher ceiling of damage.
Blood Rush: +440% critical chance at x12 combo
Galvanized Steel: boosts crit chance by 110% and crit damage by 120%
Weeping Wounds: +440% status chance at x12 combo.
Primed Smite Grineer/Corrupted: multiplicative to base damage (condition overload) and double dips status procs. Possibly triple dips the toxin status created by the AOE burst (needs testing).
[Galvanized Elementalist]: boosts status damage by 80% and status chance by a further 120%. Ideally offload attack speed or other mod to be able to slot this.
Primed Reach: gives +3m range which allows you to hit more enemies per swing
Primed Fever Strike: adds 165% raw toxin dmg and also boosts toxin statuses
Discpline's merit: consistently gives tennokai every 4 hits, can also use Dreamer's Wrath