Each season features several unique rewards. In the Pirate Season, you can obtain the following rewards if you have a Gold Pass:

Treasurer’s table (Level 20)
   
At the treasurer’s table, you can exchange 500 coins for 25 diamonds. 
You can use this item a limited number of times. After that, it turns into a decoration.

Pirate bath (Level 45)
   
Pirate bath allows you to use 3 hibiscus flowers to receive 50 energy.
This object can be used only 30 times, after which it will turn into a decoration.

Pirate organ (Level 70)
   
The pirate organ allows you to spend 5 energy to play a match-pair mini-game where you need to find two matching cards with a musical clef symbol.
If you successfully match the cards, you’ll receive some experience, coins, diamonds, and growth elixirs.

All players can also receive this special seasonal reward:
pirate outhouse (Level 70)
   
In the pirate outhouse, you can use 3 palm leaves and 1 energy to produce 3 growth elixirs.
You can use this item a limited number of times. After that, it turns into a decoration.