CRUSH! CRUSH CRUSH CRUSH CRUSH! And, you know....babble...
Wait...PJS - am I better to constrict, or can I just take normal attacks with each tentacle, and do grapple damage that way? Not sure on the who iterative vs. natural attack thingy.
OOC: You only get one attack at -4 with your tentacles, not six. In this case you only get one attack either way, but you have a better chance to hit and get constriction damage.
A 1 was not required to fail the Concentration check. The DC for the check was 23 because Luparo is grappling. There is also no reason to cast defensively while grappling if there is not a second opponent that is not grappling.