In a blender or food processor, puree the pineapple, tequila, agave, lime zest and juice and salt until smooth.
Fill the paleta cavities half-way with the pineapple mixture. Divide the serrano between each cavity, then top with more pineapple mixture. Leave a ¼ inch between the filling and the top of the mold—the paletas will expand as they freeze.
Using a butter knife, gently swirl the pineapple mixture to help the chiles evenly distribute. Insert wooden ice pop sticks and freeze until solid, at least 4 hours and preferably overnight.
To serve, dip the mold in hot water for a few seconds, then unmold the paletas. Enjoy!
MAKE AHEAD The paletas can be stored in the freezer for up to 1 month. Unmold, then store between sheets of parchment paper in a large resealable plastic bag.