To get poison, on the first level, pick some of the red and white mushrooms from the location where you get your first creature, then take all but a little bit of food from your village store and put it to one side. then put one of the mushrooms in with the remaining food. This will poison the whole stock of the store so be careful. Take the poisonous food and put it out of the way of your villagers. To get more poison food, just add more from the unpoisoned supply. Remember, poisoned food will not be poisoned when it goes through a vortex. Put white and red mushrooms in instead.

Flaming cannon ball
A little bit more fun... Break up a boulder into small chunks and casts a fireball on the after you put them into a pile. They will keep burning as long as they are touching each other. These rocks make great ammunition as they deal physical and fire damage at the same time. They set fire to fields and people and crush buildings.