Special Event Bosses

Some Events have special Boss fights we need to keep in mind.

Brewfest:
- https://tbc.wowhead.com/npc=23872/coren-direbrew
- https://tbc.wowhead.com/item=37828/great-brewfest-kodo

Hallows-End:
- https://tbc.wowhead.com/npc=23682/headless-horseman
- https://tbc.wowhead.com/item=37012/the-horsemans-reins

Start by locating how this progression system represents seasonal events and boss encounters; the issue names no files, tests, or entry points. Use the Brewfest and Hallow's End NPC and item links as the requirements, and confirm with maintainers what behavior and completion criteria are expected.

Written by the indexing model from the issue text.