I think I discovered a way to probably make an infinite amount of souls. It's not a glitch per se, just using the game mechanics so I hope it's okay to post it - if not, please delete the post (not me ).
The following happend to me today: I was invaded by a guy whom I killed, got 166k souls. He probably got his green blop and invaded me again, got another 166k by killing him, he did this a 3rd time and guess what, 166k more in the pocket (yeah he was resiliant).
So this was a random guy whom I didn't know. But what if I'd repeat this with a friend in an area where usually no PvP is going on so we keep on invading each other? First I kill him several times, then he me, then I him again, rinse & repeat. We would both end up as billionaires pretty quickly or do I miss something?
(oh and I don't have any friends who play DS so this is just a rhetorical question for me;))