The Doomsday Challenge consists of 1 general rule: Don't run out of rings, or you'll die.
This challenge puts the player into a super form instantly upon starting a map, except your ring supply is limited.
You start with 20 rings, and although that sounds easy the later zones will prove quite the challenge.
Boss levels are the only exception to the above, where the player is given more rings to compensate the lack thereof.
The player will also receive 25 rings if they collect an Emerald Token.
All of the above is only while factoring the defaults, however.
By typing certain variables into the console, you can have a much more customizable experience.
The variables are:
ddmaprings - Can be set between 20 and 50; The amount of rings the player starts with in a regular map.
ddbossrings - Can be set between 40 and 80; The amount of rings the player starts with against bosses.
ddlbossrings - Can be set between 60 and 100; The amount of rings the player starts with against longer bosses (Such as Fang or Egg Colosseum in CEZ3.)
ddfbossrings - Can be set between 110 and 150; The amount of rings the player starts with against Metal Sonic and Metal Robotnik.
ddtrings - Can be set between 25 and 50; The amount of rings the player receives upon collecting an Emerald Token.
Have fun with the Doomsday Challenge!
Oh, and before I forget, All base characters are supported.
