Instructions
Obtain two of the same species of Pinata. Once you have lured a single member of a certain Pinata species to stay in the garden, you can either repeat the process to get a second or buy one from Miss Petula's Paper Pets store.
Visit Willy Builder and pay him to construct a Pinata home for the species of Pinata you plan on romancing. When Willy is finished building the home, reveal the Pinata house with the shovel.
Research your Pinata's romancing needs. Find out what the pair of Pinatas need before they will romance and provide them with the needed supplies. For example, a Bonboon will need to eat three Jameleons before it will be ready to romance.
Select one of the Pinatas and lead it to the other. If there is a pink heart hovering over the animal's head, it will lead to a romancing minigame.
Win the game by navigating the Pinata you control to the other without hitting too many bombs. Stumble into enough bombs, and you will be forced to try again in a few minutes. After winning the minigame, the pair will enter the home, perform the Romance Dance cutscene and Storkos will shortly deliver a Pinata egg.
Repeat the romancing process until there are seven of the same species present in the garden. Having seven of the same species will unlock the "Master Romancer" achievement.