Pokémon Go Incense Day is a new type of event. Using Incense during the event will attract different Pokémon, and the first event's theme is Shuffle.
Pokémon Go Incense Day: Everything You Need to Know
On April 19 from 11 a.m. to 5 p.m. in your local time, using Incense will attract Sentret, with a chance to get a Shiny one. You'll also be able to encounter Pokémon of different types, and each type featured will change by the hour.
Niantic has also listed Pokémon you may encounter. You will most likely be able to encounter more than the Pokémon listed, but at the very least you can expect the following:
As part of an effort to increase accessibility by playing at home, Incense has also been extended to last an hour. Using an Incense increases the spawns of Pokémon near you, making it so you don't need to go far to encounter Pokémon.
Unlike Lures, only the user of the Incense can catch the Pokémon that appear. You can also stack the effects of Incense and Lures to get a lot of Pokémon quickly.
To help jumpstart the event, a PokéCoin bundle with three Incense will be available in the shop.