When I most recently fought Momentus, I did not have a bow, and I was slashing him with my voter's sword when I was strangely drawn in to Momentus when I did not run away or use a bow. If you make a skeleton attack momentus, he will get mad and start attacking the skeleton instead of you!
If you knock Momentus too far away from you, especially in water, he will assume the distance is caused by you running away and will draw you in. I've seen this happen several times when I knock him too far and then get drawn away fighting the Enraged only to have him pull me back to him.
I was only 5 or 6 blocks away from Momentus, in a desert, in a tiny sand castle to help me, and I got a lot of damage.
