Suppose as a pitcher I have a three-pitch arsenal (e.g. fastball, curveball, slider) and I play the position of relieving pitcher. I've noticed that my pitching style becomes repetitive due to my relatively low number of choices. Eventually, because my style becomes repetitive, batters will "figure me out" too easily and will figure out where to swing and when. Assuming aforementioned batters are experienced enough, they should already know this, and I am careful with them due to this.
My pitch velocity is higher than that of some of my other teammates, and I am capable of just barely clipping the edge of the strike zone with any of my pitches, making me a decent pitcher by the standards of my league.
What strategies could a pitcher with limited arsenal use to become a more effective and unpredictable pitcher?