Here are some ideas for the game:
Different mortar shells (each has own mortar)
1. Standard shell: Is good against castle walls and towers
2. High Explosive shell: Is good against a lot infantry, sort of good against castle walls
3. Poison shell: good against infantry, poisons infantry and animals in a radius of your choosing
Poison trap: will poison the person who walks over it (lasts 2 times before being destroyed)
Overall, it is a really good game! I also supported it on Steam Greenlight! :D