even without the gem the only way to actually kill Drax is with mental assaults....... or the turtle theory....... so it may only be Surfer or Cable who can take him out....... either that or they gang up on him and pull his legs off
I still put my money on Drax because of the unkillable factor and if SS could do the turtle thing, then why hasn't he done it to Drax the numerous times they clashed? Drax at one point bashed SS because he wanted to fight Thanos by himself now SS got pissed and blasted him away miles away, but he never turned him into a thing like that.
My money is Drax.
he probably didn't do anything like that because he isn't know for flagrant use of his power.... he doesn't want to kill or seriously harm anyone, hence, no turtlising