Well, the way you're supposed to get the big breasts before unlocking the debug room is to game over to the wrestling dude, which gets you the special animations as well. You can game over to every boss for a unique scene, and considering that you can teleport to any boss you've seen using the last option on the statue, there's really no reason to no just lose to them all. Make sure to lose to the scientist dude's skeleton monster if you're into futa, doppelgangers, and/or futa doppelgangers.
As far as unlocking all the skills goes, you just get them for triggering each animation X times, which specific things growing specific skills. Though, as far as I can tell, most of them just raise your pink lewdity meter. The second one is the seduce-lookin' thing, the third is masturbation, and I don't think any of the other ones do anything too special.
Maybe some of them will be given more use in later updates? I don't know if this game is going to get any new content post-release or not, but considering how few of the weapons I have unlocked after beating everything and buying all the shop items, I'm hoping that those are unobtainable because more content is on the way. It's also very possible you just get them from clearing the game on higher difficulties or for getting far in endless, but I'm gonna stay hopefully ignorant.
Also, there's a different animation with the final boss if you fight her in futa mode (or you can just see it in the dubug room) but you can't normally leave the futa room while keeping the cock. It's kinda weird to have a scene like that implemented when you have to use to debug room to set your state to futa to see it, since doing so makes clothes kinda buggy when doing certain actions and most monsters just ignore futa. It feels really unfinished and I hope it's there as a sneak peek for new stuff rather than just a leftover animation he left in the game for us.
Power of positive thinking and all that.