I just had a strange encounter with Momentus in the Wasteland on SMP9. At +/- 9:51 PM EST on Saturday, August 2nd I attacked him at approximately position -3531, -181 according to Dynamap. I hit him one time and Momentus died immediately from a single stoke from my diamond sword. There was also a single Enraged Zombie summoned which I quickly dispatched. Momentus did drop 2 dragon stone fragments, 2 zombie heads, and 8 shiny flesh which seemed pretty reasonable. However, I only received a total of 22 tokens. My difficulty level was set at 5 and I had received in excess of 1600 tokens when I battled him a time before. The previous encounter also took much longer. I had been in the Wasteland for quite a while and had not seen anyone on Dynamap in my vicinity who might have already attacked and weakened Momentus and I was a long way from any Outpost. In any event, I looked for an admin and didn't see any so I thought I'd report my encounter this way. Thanks for your attention.
Someone could have weakened him before, possibly dying so close to the end, as I believe mini bosses don't despawn once engaged by a player. The low tokens would be a result of you only doing a tiny amount of the total damage.