From Guild Wars Wiki
Seasonal items are items that can be acquired during some special in-game events. Seasonal items that drop from PvE foes are exempt from loot scaling, and can be solo-farmed very effectively.
- Non-boss foes can drop one of each seasonal item at the same time (e.g. a Chocolate Bunny and Golden Egg during Sweet Treats Week).
- After the end of a special event, seasonal items will continue to drop in instances that were entered before the end of that event.
- In PvP, Guild Lords always drop seasonal items during certain special events.