(A number of these captures first appeared in the Easter Eggs theme page.)
The first instance of Katze almost unmasked: Makoto's "father" takes off his face. I hope he has another false face underneath or the goons in that mecha are in on the secret, else he's in trouble. Not that any of his men survive the mission...
A disguise scene: Katze tosses off the cloak and starts to lift off the mask. What a moment for the camera to change scene! (BTW, no reflection in the mirror; did the animators realize they are suggesting that Katze is a vampire?)
That split second when Ken's boomerang whizzes over the mask and slits the nosepiece.
The first attempt to unmask Katze: a spontaneous impulse on the part of Condor Joe who gets a knife stuck in his wrist for his trouble. (But he gets his revenge in ep 102.) Does anyone else notice a small animation goof?
Oh, alright, same scene again without the animation goof. This is before Katze gets the scalpel. Joe, never one to beat around the bush, goes straight for the mask. Katze tries to pull him over his head.
A second and more successful attempt at unmasking, this time by Ken; it's a pity that this is all they get to see.
But in the end it is Katze who does the job, or rather his anti-Birdstyle weapon does it, by firing backwards when Joe plugs the muzzle.
After the final unmasking, does s/he really change gender before the team's eyes? I doubt it. I fear the turning-around sequence was simply drawn by novice artists and only the part where s/he addresses the stunned ninja team, by someone who could draw. Here's a few shots from the sequence, judge for yourself...
The villain is unmasked, and it turns out to be... Egobossler? A little green man? A bug-eyed monster? A humanoid cat? Or just someone who didn't sleep well lately?
The final confrontation. By way of comparison, here's a pic of the female form in the same episode, showing the flat and rather femmy stereotype used from ep. 88 onwards; maybe the animators were getting fed up with the character?