Very nice card idea,
I was just thinking of repeated applications.
If Slow was used twice on one creature would that reduce it's current attack to 0, or 1/4 (depending on rounding) of it's max? In other words would you use the full or the current attack to calculate the effect?
I don't know if this fits with your concept very well but the idea of using the stop effect twice to create a negative attack would be interesting I think.