With a partner.
20 4-Count Flutterkicks
Invisible Wall Sit, plank or stand with 2 KB/DB's locked out overhead.
While partner 1 does the calisthenics, partner 2 holds the invisible wall sit or other isometric holds. Then they switch, until they have each completed the calisthenics portion 4 times. The faster the one partner moves, the sooner the other is done holding positions.