When placed on the ground and lit with a Torch or a Lighter, the Flare will shoot up into the sky. It then creates three flare marks on the map, unlike a normal Flare that only creates one mark.
After activation it has a chance to spawn various enemies. There is a 60% chance to spawn Deerclops and/or an existing MacTusk hunting party near the player when used on land during Winter. If used on a Boat with no Monkey Pirates nearby, a Pirate Raid has a 60% chance to appear.
Players can use the Hostile Flare to fight Deerclops more than once per Winter season, with the goal to acquire more than one Deerclops Eyeball. This allows for crafting of several Eyebrellas and Houndius Shootius without the need to wait for subsequent Winters.
If the Hostile Flare is used to summon and kill Deerclops, it will reset its spawn timer of 71.8 days.
Trivia
The Hostile Flare was added as part of the One For the Books update.
Bugs
Currently, regardless of resetting the timer of Deerclops, it will still spawn on its designated day.