flying enemies and secret opening

I have 2 questions:

How to make flying enemies?
How to make a secret opening?

I’ve been trying all morning and I can’t figure it out.

  1. Disable Gravity for that object
  2. use alpha to make things invisible

@JR 01 but what if i want to make the visible again

You use a number from 0 to 100;
0% - Invisible
100% Visible
1-99% opaque value

You can change the values anytime