Was fighting the Enderdragon yesterday on 15w43 and at times I had huge deathly lag spikes - I died enough times as it was!

I spent a long time getting the last crystal (once I had got this, the rest was easy). It seemed that very time I would try and pole up to the the top of the pillar she come in an knock me off. If I was at the bottom she would breathe on me and I had to run outside the effect of the dragonbreath cloud. It was at these time I would have the lag spikes - I managed to get a couple of sceenshots and I've attached these.

This could be related (a consequence of) MC-91225 <i>Items have a lag before visually teleporting</i>, endermen were running around screaming at the same time and most likely teleporting.