Necrolai on Sledge's ship
I know that Necrolai being in the background as one of the prisoners on Sledges ship was a case of Saban reusing old costumes but could there be another answer?
Maybe Sledges ship uses some kind of temporal leghtspeed engine that causes everyone on his ship to not age very much while time moves normally on the outside.This would explain how Sledge and his minions are still alive millions of years after wiping out the dinosaurs..
Maybe once sledge is defeated at the end of this season the rangers cause his ship to begin to explode.Causing an evacuation with the prisoners some how breaking free from their cells and going into numerous escape pods.
Cue scene where Sledge's ship explodes as the escape pods are caught up in the temporal explosion sending all the pods into differant time periods in the Power Ranger saga.
Like we get to see Necrolai's escape pod crash down into Briawood where she is found by Morticon and the Master so she ends up joing their forces.
The same can then be shown with other reused moster costumes such as Monkeywi's pod crash landing in Ocean Bluff ten tousand years in Earths past where he is found by Grizzaka.
It would make for a nice bit of continuity for long time fans.
Its treason then! (Palpatine - Star Wars ROTS)