Fun nerdy writing exercise.
I bought 4 tiny corked bottles. I wanted to make potions for D&D. So I brainstormed a variety of colours and substances, wanting a good color spread, and used colours as inspiration for what the potions could do.
A bit of creative problem solving gave me some options, some crummy, some fun, and it was a good ten minutes of thinking for an awesome cause.
Now I have 4 potions I can use when I run adventures at school, and out of school.

Plus: a bottle of blue liquid can be a different spell in every adventure it appears in, requiring more creative writing from me, and critical thinking to match the effects of the potion to the specifics of the narrative.
