Mastering Enchanting allows you to create custom magical items with powerful effects, either constant or on-use. Similarly, at a Mages Guild, you can create custom spells by combining existing spell effects. This allows for incredible versatility, such as 'Soultrap on Target' for easy soul gem filling, or 'Fortify Strength 100 points for 1 second' for massive damage. Experiment with spell effects and magnitudes.
