First challenge battle of the fireworks event!
Overall this battle has a relatively low power requirement. Your fielded team composition can also be quite flexible.
I mainly used two units to damage the boss and all of my other units sat around waiting for the adds to spawn.
The core mechanic of this fight is the "Tinder" buff. This buff is obtained by having one of your units step into the blue flame at the start of the battle. "Tinder" lasts 1 turn and will jump to a random unit directly next to it at the end of the action. This means you always need to end the turn of your "Tinder" buffed-up unit adjacent to another unit. You MUST have the tinder buff on one of your units at the end of your turn. If you don't the boss will just instantly wipe your team.
This boss also only takes damage from a unit with the "Tinder" buff so you will need to rotate the units you have attacking the boss. Keep in mind that all of the boss' abilities has a random dispel chance and you can potentially lose the "Tinder" buff to an AoE from the boss or even an attack from the spawns.
Due to the relatively low stats of this boss you can take it slow and take your time to chip away at the boss.