A beehive puffer based on this spaceship was found the same day, seemingly independently by iNoMed and GUYTU6J. GUYTU6J also found a block puffer formed by adding a second weekender to the side of the p21 ship. Both of these puffers can be either one- or two-sided. Various glider rakes have also been constructed. On December 7, GUYTU6J and Aidan F. Pierce found several period-42 doo-dah-based spaceships.
Goldtiger997 found that the p21 tagalong could be added to the weekender with six gliders, while iNoMed found that each side could be turned into a beehive puffer with two gliders. Finally, gooddogtyson and Blinkerspawn found that the p21 ship could be converted both to and from a puffer with just one glider each way, on each side.