Well as we all know Blue creepers are innocuous (they don't explode or do damage, so are just easy gunpowder/sulphur sources), normal Green is normal and Red should be 1.5x blast radius. We could have Orange creepers that have a 1.5x blast radius but no damage, and Purple that do 1.5x damage in the normal radius but no actual blast.
Then we have boss creepers, 'Mach 2' Creepers, Dark Green and 5 times normal size that only spawn on Hard, and in Plains biomes. They travel in flat lines and will rarely ever jump. They destroy blocks in front (all blocks touching its hit detection area) of it at the rate of 2 blocks forward per second. They will also automatically aggro any player within a 25 block radius. Their blast is huge, creating a huge crater about 7x the normal size, but does much less damage. Their main damage output is though shooting fireballs at the player in a Ghast-esque manner, but when they run out of health they health they will explode. They can take 50 hearts of damage, giving them half the Ender Dragon's health and 33% of the Wither's health. They can, therefore be classed as a mini-boss. Upon death they will drop an Emerald block, a Creeper skeleton (or a Mach 2 Creeper skeleton could be implemented), and a Diamond block.
There would then be the new 'Gunpowder Dimension', an island which can be accessed by creating a portal in the same fashion as a Nether portal. The main difference is that the portal is activated by placing a Mach 2 Creeper skeleton to light the portal rather than with flint and steel. The roughly 300 by 300 island the player lands on is inhabited by Creepers only and of all kinds (excepting the Mach 2). In this area creepers have a 1 in 25 chance of dropping pure TNT, and can be used as a great area to acquire masses of gunpowder and TNT before heading off to BLOW STUFF UP.
That's about it. Thoughts?
