One thing I wanted from the beginning was a variety of spells & powers to customize your individual characters with. Keep in mind the game did not start out as a collectible card game and my main inspirations were rpg & tactics games (fantasy/ogre tactics). So, the first thing I did was make the individual characters (your army) very customizable. Lots of classes, spells, items, etc.
So I'm going to talk about character customization and such here first...before the cards/runes themselves (which was a later invention).
I started with about a 100 spells ranging from things like damage spells, to ability score boosts, to healing, to summoning, etc. I got most of my motivation/ideas for these spells from fantasy games I had played (heroes, age of wonders, etc) and dungeons and dragons. I would basically take a spell name, alter the name if necessary (not too specific), and then make the spell applicable to my game somehow.
Early spells include Frost, Resist Magic, Silence, Boulder, Venom, Rock Shards, Sun Dragon, Summon Demon, Dominate, etc.
Later I felt I needed more variety and found inspiration from collectible card games (Magic the Gathering primarily) to create about another 100 spells. I decided to add a lot more summoning spells and introduced "avatars" into summoning. New spells include Dark Ritual, Panic, Shield Wall, Mental Library, Anaria Re, Icy Prison, etc.
Do other people borrow there spells/power ideas from other games? Things like names of spells and basic concepts? Keep in mind I changed everything but I still got the initial idea and possibly the name straight from a specific source.
I originally decided to use a kind of spell scroll for characters to view and cast spells from. I used a bit of clip art for this. I decided spells would simply be text. Here is a look.
This brings me to my choice to change the game from more of an amateur project to a professional one. But I get ahead of myself. That will be the next subject. For now here is a picture of the new spellbook (not quite complete and an old screenshot) to see how it has progressed.