It's nothing super or overly pretty, but I've been working on this one spell for my AoS map that's pretty handy.
It's for a hero called the Samauri, and the skill is called Seppuku. In total it has 5 levels in total and works as a charge up skill. Every time the hero uses it, it gives him a bonus of some sort. If he uses the ability again before it's timer expires, the bonus are boosted and the expiration timer is reset.
Seppuku costs no mana, but it does suck up 50 of the Samauri's health. When innitially cast, his movement and attack speeds are increased by 30% and all magic damage he takes is reduced by 20%. The effect lasts 15 seconds. If the Samauri uses Seppuku again before the last charge expires, his movement and attack speed bonuses are boosted by 10%, while the magic damage reduction is increased by 5%.
At level one, Seppuku bonuses can only be stacked 3 times. Upon reaching 50% speed and 30% magic reduction, additional uses of the skill only reset the timer. Each skill point invested in Seppuku boosts the stack limit by 1. At level 5, Seppuku bonuses can be stacked up to 7 times. That's a total of a 90% speed and a 50% magic reduction. Of course, getting that high does cost a bit of health; 350 to be exact. | 
