Kicking on your side with your face in the water lift your top arm in the air, palm facing forward. Hold it for a short time, then hinge at the elbow, pause, then spear your hand into the water in-line with the same shoulder, parallel to the opposite arm. As your hand spears forward rotate to the opposite side and inhale with both arms still for a moment. Repeat.
Brilliant for balance, posture, strength, arm recovery, working on where your hand enters the water and isolating how it enters. Build up to it with kick on side arm in air and broken -broken arrow drills first.