If you are lucky and rich enough to collect all ten of these exclusive items then you will be able to unlock the Ultra Rare Nu Life Poolside Assistant Writing Skill Item that is worth 59 SimCash and will raise your House Value by +8700. We'll have the full details on this item in a future article, you will be able to use the 'Search' bar via The Sims Social Fansite to find it once it's written.
If you want to attempt to buy these new Pool Theme Mystery Boxes the simply click on the brown Mystery Box icon in the top right of your The Sims Social game screen or you can claim your Free Summer Party Mystery Box here! It doesn't look like Playfish have changed the way Mystery Box items are received and duplicates are still possible.
The ten Summer Party Mystery Boxes consist of 3x Rare, 3x Uncommon and 4 Common items. Here is a complete list of all of the items available along with the House Value, classification and recommended SimCash value:
Summer Party Mystery Box COMMON Items:
Charmed Toad Statue, Bubble Lights, Nu Life Garden Shade, Gaia Potted Banana Tree
Summer Party Mystery Box UNCOMMON Items:
Seafaring Seahorse statue, Nu Life Fountain, Dolphins Wanna Have Fun
Summer Party Mystery Box RARE Items:
Bahama Hanging Chair, Bahama Curve Lounger, Nu Life Fireplace