A very popular extended technique on mallet percussion, particularly marimba, is using the shaft of a mallet to hit the edge of a key.
To achieve this, a player must play on the near side of the natural keys, and the far side of the accidental keys. It’s a little awkward no matter what, with playing solely on the edges of accidentals being the easiest combination. Playing on both registers (example 2 below) adds a challenge as the player must reach much farther on the vertical access than normal. Rapidly switching between normal and shaft playing with one hand (example 3 below) is quite a lot of work and will quickly become very difficult beyond a slow tempo, as the hand will have to move constantly between its normal position and an altered, angled position needed to strike the key appropriately.
Some of academia’s favorite marimba solos employ a good deal of this technique. Check out Joseph Schwanter’s Velocities and Leigh Howard Stevens’s Rhythmic Caprice to listen to this technique in context.