I thought it was 24 to trigger the Killer Bunny...? Whatever the number, it's harder to obtain it in DKS.
I noticed a significant decrease in the bunnies. As soon at you get to Broken Valley, there were 2 bunnies around the teleporter in ED, there isn't in DKS. That's just one place I remember...though I assume there are way more. ^^; In ED I faced the Killer Bunny before ever getting to the Wishing Well. In DKS I fought the bunny after completing Maxos Temple.