Niue, a sovereign state in free association with New Zealand, uses two official legal tender currencies. The New Zealand Dollar is the circulation currency for daily transactions, while the government also authorises legal tender coins in the Niue Dollar currency for collector's purposes.
A number of mints issue a large variety of commemorative, bullion and collector coins under the authority of Niue. These coins are dedicated to historical or general popular culture themes not related to Niue itself. Many of them are made using "smartminting" techniques and have features not generally found in circulation coins - e.g. high relief, full colour printing and/or different forms, including fully three dimensional (3D).
Some coins are marketed in standard bullion sizes, like half ounce silver, one ounce silver etc, and some of those are also denominated as $1, for which see respective lists; this particular coin denominated as One Niue Dollar is not in a standard ounce-based size.
The mint says about this coin:
According to the Chinese calendar, the Year of the Pig begins on 5 February 2019 and ends on 24 January of the next year. Pig, the twelfth animal of the Chinese Zodiac, is a sign of responsible and open-minded individuals who are sincere, devoted and friendly. People born under the sign of the Pig particularly value relations with other people; thus, they surround themselves with a circle of loyal friends. | 
Search for Niue: One Dollar Silver 2019 Year of the Pig - Seven Elements on eBay 