The Power Rangers universe was built on crossovers and cameos, many of which came out of nowhere and helped build a sense of continuity that made the show even better. When it comes to special appearances in Power Rangers, there is a difference between the usual crossover episodes between the current and the previous team, and cameos from legacy heroes. Almost every season had one team-up episode featuring the previous Power Rangers team, but not every season had cameos from other generations.

https://screenrant.com/power-rangers-best-cameos-list/