As You Command OOC

[Waistcoatwill]

Isn't picking up an item in 3.5 a move action that provokes an attack of opportunity? So the hippocampus might only be able to do a normal move action after it grabs the chain rather than withdrawing.

Cypher only gets one AoO per round, but either way he should probably get one before the hippocampus starts moving again.

Edit: 15 to hit on that Hail Mary, oh well...last turn of haste this round, I'm guess the hippocampus will have moved out of his range though, is that right? Otherwise all that's left is to power attack the chain and hope to crit. Attempting to grab hold (being dragged) and pick the lock underwater sounds impossible.