As a bat, the map is zoomed out, the player gains a configurable movement speed bonus, and the player can pass through obstacles unimpeded.
There are options to restrict transformation to outdoors and at night, and an option to set a stamina cost per second while transformed.
Config
You can customize this mod by editing the config file or using Generic Mod Config Menu.
Technical
Requires SMAPI.
Implements a Generic Mod Config Menu interface to change config settings in-game.
Compatible with Mod Updater for automatic updates.
Code is at https://github.com/aedenthorn/StardewValleyMods.
If you want to complain or ask for help or help me test my mods, you can visit my Discord server.
A list of all my mods for Stardew Valley is available at https://www.nexusmods.com/stardewvalley/articles/895.