From Dota 2 Wiki
- Vials appear as items in the armory, as a tool.
- River vials can only be used in matchmaking. They cannot be used in lobbies or in custom game modes.
- Upon using a vial, a global Play sound effect plays and a message appears on screen, reading: "Player has painted the river with River vial: type!".
- When standing within the river, a pop-up appears on the right side of the screen, showing the available vials. Clicking on a vial applies it to the river.
- The altered river appearance lasts 3 minutes.
- A vial can only be used once per match.
- Vials are not expended on use and can be used again in a new match.
- While in-game, the player must purchase the vial from the shop. It is a consumable with 1 charge. It can only be used while standing within the river.
- The altered river appearance lasts 15 minutes.
- Using a vial consumes one charge from the tool in the armory.
- Once all charges are spent, the tool disappears.
- Charges are only consumed if the river effect lasted its full 15-minute duration.
- Charges are not consumed if they are overridden by a stronger vial, or if the game ends before their full duration.
- Rarer vials are considered "stronger" than more common ones.
- Using a stronger vial will override an existing effect from a weaker vial.
- A weaker vial cannot be used if a stronger vial is already in effect.
- The following is a list of vial priorities, from strongest to weakest:
Rank River vial 1 River Vial: Blood 2 River Vial: Potion 3 River Vial: Electric 4 River Vial: Oil 5 River Vial: Slime 6 River Vial: Dry 7 River Vial: Chrome