Thought I'd make this topic to keep track of how many enemies and loose rings there are in each stage and the average amount of rings needed from enemies for 999 rings (whether or not 999 is probably possible). I've done Seaside Hill already since my next goal in Heroes is to max it. Here is the stuff I found and tell me if you get more or less enemies, average, and/or rings:
Rings: 363 (this includes the single ring past the last crab)
Enemies: 45
Average from enemies for 999: ~14.16
This means you will need mostly 10s and 20s to get 999. If you get more than half 20s, you have room for a 5 or two. I could be wrong but that is what i think :/ Anyone else wanna help with the rest of the levels? Really, I don't think Grand Metropolis and Power Plant are neccesary to keep track of because they are very easy to max.