The 3500% ROI is because blocks were coming in way to fast for that day, they were calling it a "blockspike"

Actually there is a serious bug in the re-targeting algorithm that means block times can be really fast sometimes (and other times really really slow) which is really not good at all.
As its in the targeting algorithm they will need to hard fork (and likely do a coin swap) in order to fix it.

oops!