Kakabakaba (Insect and Monster Transformations)

 Thanks to Ian Ricky for going through the episodes of this old Filipino fantasy series. 

In the first clip a merman creature who had taken human shape reverts to its true form (at 03:20)

In the second clip a cockroach alien has invaded earth and disguised himself as a young man. 

At 02:52 he reverts to insect form, and again at 04:04, and at 05:00. Finally, he reverts to his more feral form at 05:27.