Inspired by similar Pretender work on tfw2005 by kraegorstark - it's Pretender Bludgeon!
I used a Thanos mechtech figure on discount at Toymate.
I was going to make it a CHUG figure - and yes, legacy Skullgrin can be made to fit - but thought it looked too cartoony so bashed together the inner robot from my Cyberverse/RID2015 leftovers.