I've noticed that some moves have a lower drop rate than others (like BB3s) but forbidden procedure seems to almost never drop.
I’ve been playing since about a month after SGM hit the app store and in the past (what, three years?) I’ve only managed to get 3 gold versions and I think 2-4...
I have a gold level 7 Forbidden Procedure on my gold icy hot valentine. The very first time I used it it worked like a charm. But ever since then I have used it countless times and it hasn't worked since. I've lost so many prize fight matches because the revive wouldn't work.