I'm afraid you are in error Mr. Spaz. Evil Otto WAS a robot master. He was simply made out of liquid metal not unlike T-1000 from the Action movie known as Terminator 2.
His ability to go through walls was just a quick way of showing how he could slide through the smallest of cracks due to the material he was built from. This of course was not able to be shown due to the primitive graphics during that time, but it was implied.
And you were able to kill him in Frenzy. It took three shots and his face would change like so:
:/
But after his apparent demise he just kept coming back faster on the other side of the screen faster than ever, until you couldn't keep up anymore with attempting to kill him. Again not unlike T-1000. I believe he must've been based on Evil Otto.
Calling me a merengue will accomplish nothing Mr. Spaz. Interesting insult though. Did you have a bad experience with that particular food substance, causing you to consider it a demeaning insult now?