Quick answer
The event is friendly for getting something, not friendly for guaranteeing the whole outfit.
Every Summer Treasure Key opens one Summer Treasure Chest. The chest has a 2% total costume rate split across four Beach Party pieces at 0.5% each. I do not see a client-side pity or guarantee table for this chest, so write the player advice as odds-based rather than guaranteed.
Chest odds
Summer Treasure Chest reward table.
The chest mostly gives the three summer treasure exchange items. The Beach Party costume pieces sit at the bottom of the rate table.
| Reward | Count | Chance |
|---|---|---|
Jewel Powder
|
10 | 70% |
Jewel
|
1 | 22% |
Jewel Assortment
|
1 | 6% |
|
|
1 | 0.5% |
|
|
1 | 0.5% |
|
|
1 | 0.5% |
|
|
1 | 0.5% |
The duplicate replacement row uses the internal currency code FreeDia, which displays as Red Diamond. A duplicate Beach Party piece converts into 3,000 Red Diamonds.
Key plan
Count deterministic keys first, then add optional recycling.
The safest estimate separates guaranteed event keys from chest-open rebates and exchange-shop recycling. The exact daily total can shift by server-day timing, so treat the daily mission line as an event-window estimate.
Summertime 10-Day Attendance gives four 5-key days and four 10-key days.
Pop! Water Balloon total milestones give 10 keys at 5,000 and 20 keys at 18,000.
The daily Elite Monster mission gives 1 key per day across the event window.
Play-count milestones give 10 keys at 5 plays and 15 keys at 15 plays.
Treasure Hunt gives 10 keys after 40 opens and 15 keys after 120 opens.
5 keys per week at 800 Red Diamonds each, assuming seven weekly windows before July 23.
Optional Jewel Powder recycling Useful, but not clean enough to call guaranteed.
Treasure Exchange has a weekly key exchange that costs 50 Jewel Powder for 1 key, with a visible weekly completion requirement of 5 exchanges. Because Jewel Powder comes from the chest, this is a recycle loop: it depends on your rolls, reset timing, and whether you spend powder on keys instead of other exchange rewards.
At about 217-218 openings, direct Jewel Powder expectation is high enough to approach the 35-key event cap after recycling, but variance and spending choices matter. If you count the full recycle cap, the model lands near 252-253 openings instead.
Diamonds
Red Diamonds buy weekly keys. Blue Diamonds buy direct keys and hot deals.
Weekly limit is 5 keys. Seven weekly windows would cost 28,000 Red Diamonds for 35 keys.
The row has no visible buy limit in the local client table. Use this as paid chase math, not a value recommendation.
Duplicates convert into Red Diamonds, not Blue Diamonds. This only helps after you already hit a costume duplicate.
Hot deals
The two Treasure hot deals add keys, but they still do not guarantee the outfit.
Only the Summertime Treasure hot deals that directly include Summer Treasure Keys are listed here. Other event hot deals do not change the key math, so they are left out.
| Hot deal | Rewards | Keys | Limit |
|---|---|---|---|
| Cool Summertime Treasure Hot Deal | 9,000 Blue Diamonds, 20 Summer Treasure Keys | 20 | 1 |
| Sizzling Summertime Treasure Hot Deal | 15,000 Blue Diamonds, 35 Summer Treasure Keys | 35 | 1 |
Do not buy these only because of the outfit odds. Buy only if the Blue Diamonds and other bundle contents already make sense for your account, then treat the keys as extra chance.
Odds table
What the key counts actually mean.
These estimates use the visible reward rates: 2% for any costume piece and 0.5% for each specific piece. Full set odds use the four-piece coupon-collector calculation, not a simple 2% roll.
| Opening count | Scenario | Any costume | Specific piece | Full 4-piece set |
|---|---|---|---|---|
| 60 | Attendance only | 70.2% | 26.0% | 0.4% |
| 157-158 | Earned event keys before rebates | 95.8-95.9% | 54.5-54.7% | 8.7-8.8% |
| 182-183 | Earned keys plus open-count rebates | 97.5% | 59.8-60.0% | 12.7-12.8% |
| 217-218 | Add Red Diamond weekly shop | 98.8% | 66.3-66.5% | 19.2-19.4% |
| 252-253 | Add expected Jewel Powder key recycling | 99.4% | 71.7-71.9% | 26.3-26.5% |
| 272-273 | Add both Treasure hot deals, direct keys only | 99.6% | 74.4-74.5% | 30.5-30.7% |
| 304-305 | Also spend hot deal Blue Diamonds on 2-key products | 99.8% | 78.2-78.3% | 37.3-37.5% |
| 400 | Heavy chase benchmark | Almost 100% | 86.5% | 56.0% |
| 600 | Very heavy chase benchmark | Almost 100% | 95.1% | 81.6% |
Any costume: 1 - 0.98^keys. Specific piece: 1 - 0.995^keys. Full set: 1 - 4(0.995^keys) + 6(0.99^keys) - 4(0.985^keys) + 0.98^keys.
Costume stats
The Beach Party pieces have collection stats, but the outfit is not worth panic-buying for stats alone.
Owning all four listed pieces adds Main Stat +80 and Bonus Gold +40% through collection stats. That is nice, but the full-set odds are still the main caution.
Guide notes
How to explain this to players.
Use Red Diamond weekly keys if the event matters to you.
They are the cleanest non-cash key source, but they still do not make the full outfit likely.
Do not frame the hot deals as outfit completion packs.
The two Treasure hot deals raise the odds, but the full-set chance is still far from guaranteed.
Say "no visible pity" instead of overclaiming.
The local client data does not show a pity table for the chest. If Nexon documents one elsewhere, update the page.