Aealic Harmonizing Stone

On paper this sounds like it might be the best general-use 9.2 optional reagent for combat.

If you craft this on ilevel 233 gear, the gear's tooltip indicates that it gives +32 primary stat for 15s. You should theoretically be able to stack this up to 12 times with 12 pieces of gear with this enhancement (13 if you're an alchemist with the trinket). The other progenitor enhancements I've tested stack like this, I haven't been able to actually test this one yet.

The other optional reagents that have combat use are:

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• Magically Regulated Automa Core - "Your abilities have a chance to spawn an unstable Automa Core which detonates after 4 sec, dealing 258 Cosmic damage to enemies and healing nearby allies for 258." (Per spell page)
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• Devourer Essence Stone - "Slaying enemies increases your highest secondary stat for a brief moment, stacking up to 5 times."
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• Cosmic Protoweave - "Increases Avoidance and sometimes heals when taking damage."
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• Erratic Genesis Matrix - "Being struck by an enemy builds electrical sparks. At 5 stacks, the circuitry shorts and lashes out." (Deals 373 cosmic damage per spell page.)
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The other optional reagents that have utility:

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• Pure-Air Sail Extensions - "Increases movement speed and mount speed while in the Shadowlands."
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• Sustaining Armor Polish - "Increases the duration of flasks, elixirs, and food buffs."
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• Infusion: Corpse Purification - "Chance to acquire additional resources from corpses."
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Initial testing in Zereth Mortis and on the target dummies in Zuldazar. Drops small orbs that you run over like Pelagos. Varied proc rates had 3 times per minute and other times only once per minute. Orb spawns are very random and up to 10 yards away it would appear. They despawn after 10 seconds.