The Piggy Bank was introduced in 2.4; it provides an opportunity to buy gems at a discounted rate (if you fill the piggy bank, you can get 2.5x Gems compared to what you would normally get for that price in the shop).
There are different levels of piggy banks as follows, and opening up one piggy bank unlocks the next one.
| Level | Coins Needed | Gems | Price (USD) | Gems/$ | Gems/$ in Shop |
|---|---|---|---|---|---|
| Plastic | 40 | 1,200 | 2.99 | 400 | 160 (320 for 1.99) |
| Bronze | 40 | 2,500 | 4.99 | 500 | 200 (1,000 for 4.99) |
| Silver | 50 | 6,000 | 9.99 | 600 | 240 (2,400 for 9.99) |
| Gold | 50 | 12,500 | 19.99 | 625 | 250 (5,000 for 19.99) |
| Platinum | 60 | 32,500 | 49.99 | 650 | 260 (13000 for 49.99) |
| Diamond | ?? | 70,000 | 99.99 | 700 | 280 (28000 for 99.99) |
Note that because you need to spend on the less attractive lower tiers before you can get to the higher tiers, the difference between Piggy Bank and BOGO isn’t as big as you might expect. So it’s more like 8~11% better rather than x2.5 vs x2 and is only cheaper if you unlock at least the Silver Piggy Bank:
| Highest Level | Cumulative Gems | Cumulative Price (Rounded) | Effective Gems/$ | Comparable BOGO |
|---|---|---|---|---|
| Plastic | 1,200 | 3 | 400 | 400 (1,000 x2 for 5 $) |
| Bronze | 3,700 | 8 | 462 | 480 (2,400 x2 for 10 $) |
| Silver | 9,700 | 18 | 539 | 500 (5,000 x2 for 20 $) |
| Gold | 22,200 | 38 | 584 | 520 (13,000 x2 for 50 $) |
| Platinum | 54,700 | 88 | 622 | 560 (28,000 x2 for 100 $) |
| Diamond | 124,700 | 188 | 663 | N/A |
Notes:
- Prices are shown in USD; the actual prices can vary by country but you would get 2.5x Gems that you would get for that price in the shop
- It is possible to open up the piggy bank even when it is not full, but then you don’t get the same benefit so it would be a waste. Also, I haven’t tested to see if opening an incomplete piggy bank still unlocks the next tier. In any case, if you are playing often enough to want to buy gems, you shouldn’t have a problem filling up the piggies