[Tools] Item - Combinator Costrel

The act of combining chemical substances on the fly is a hallmark trait of an alchemist and designing an alchemist item that doesn't do that would be a disservice. This did end up with the unfortunate side effect of being like Honey Lemon's purse from Big Hero 6. On the flip side, during research I did learn that Costrels are a thing.

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An impressive feat of alchemical engineering straight from the development worktables of Eidorik's Laboratory, this costrel is designed to conceal its three hidden compartments, its individual contents seemingly mundane to the untrained eye. Master alchemists who understand the costrel's utility carry it deftly into secure areas, combining its contents into much more potent and deadly chemicals.

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Combinator Costrel
Wondrous item, rare (requires attunement by a character proficient with alchemist's supplies)

You can use this costrel as alchemist's supplies for storing or catching volatile chemicals. While attuned, you also double your proficiency bonus to ability checks made using alchemist's supplies. Creatures unaware of the costrel's properties initially perceive it as a simple tool and can use an action to recognize its true purpose by succeeding on a DC 15 Intelligence (Arcana or Investigation) check.

Volatile Fusion. The costrel conceals three compartments each holding one of three volatile substances: scorchpowder, winterflux, and viscigum. Each compartment holds up to 3 ounces of the substance, and you can use alchemist's supplies to replenish expended substances when you finish a long rest.  While holding or wearing the costrel, you can use an action to speak its command word and produce one of the following effects, expending 1 ounce of the substances required.  

• Bite (scorchpowder, winterflux). The costrel produces a stinging fluid you can immediately splash at a target within 10 feet of you as part of the action. The target must succeed on a DC 15 Dexterity saving throw or take 1d8 acid damage and be blinded for 1d4 minutes. A creature can end this blindness by using its action to make a DC 15 Dexterity check to remove the fluid. If splashed on a nonmagical metal surface, the fluid instead dissolves up to 1 inch of metal within a 5-foot square area.
• Burn (scorchpowder, viscigum). The costrel produces a sticky burning wax you can immediately throw at a target within 20 feet of you as part of the action. Make a ranged attack roll adding your proficiency bonus. On a hit, the target is coated in wax for 1d4 minutes. A coated target takes 1d6 fire damage at the start of each of its turns. A creature can end this damage by using its action to make a DC 15 Dexterity check to remove the wax.
• Chill (winterflux, viscigum). The costrel produces a sticky chilling paste you can immediately throw at a target within 20 feet of you as part of the action. Make a ranged attack roll adding your proficiency bonus. On a hit, the target takes 1d10 cold damage and is coated in paste for 1d4 minutes. A coated target's walking speed is halved. A creature can end this reduction by using its action to make a DC 15 Dexterity check to remove the paste.
• Foam (all substances). The costrel produces an expanding foam you can immediately throw at a point within 20 feet of you as part of the action. The substance expands into a 10-foot radius circle of sticky foam that lasts for 1d4 minutes. This foam is considered difficult terrain. A creature that starts its turn in the foam or moves into the area for the first time on a turn must succeed on a DC 15 Strength saving throw or be restrained by the foam. A restrained creature can free itself by using its action to repeat the saving throw, ending the condition on a success.