Yesterday I implemented collision detection between characters. This wasn't as complicated as I thought it'd be. But now the rat will chase the player around and stop near him and the player can't actually enter the rats area.
I also set the first action: attacking. There's currently a really terrible attack animation for the player that fires whenever the player presses the space bar. The scale of the "attack" and sword swinging is so off that I feel like I need to adjust the size of character sprites and/or use new textures for the character before continuing. It's distracting at the moment.
Once I get that taken care of I can add in dealing damage to the rat (and attack radius, etc). This will build on the methods I already developed for collision detection.
Then after that I need to start building an actual "level" with walls. That will allow me to do more complicated AI tasks such as LOS and path finding.