Idea 1
A nice setup could be the classic forbidden garden. Add some trees, a pond and the aforementioned plattform with a shrine in the middle. And if you really want to rock, giver your fey a power to shift the natural part of the environment.
Cycle of Nature
At the start of her turn XXX(insert BBEG here) uses a free action to change to the next season.
Each season would then have specific effects, so that for example in autumn, falling leaves could grant cover from ranged attacks or during summer her attacks might deal additional fire damage.
Of course, this setup would require quite a bit of work, but it would surely do for a memorable boss fight.
I'm liking this idea -have different effects for each season.
1) Spring - Thunderstorm happens - attacks that contain "lightning" deal extra damage, while those with "fire" deal less due to the storm. Ranged attacks are at -2.
2) Summer - heat wave - fire attacks deal extra damage, while cold attacks deal less.
3) Autumn - the swirling leaves make ranged attacks a -2 penalty and long range a -4. Air attacks deal extra damage due to the swirling leaves, while ____ attacks deal less.
4) Winter - blizzard - moderate acrobatics check to move beyond a shift, else you fall prone. Cold attacks deal extra damage, while fire attacks deal less.
Any suggestions on effects/bonuses/penalties?
Thanks