From what I can see on my end, your interaction works fine. Does the crash happen the moment you use it, or does it happen when you try to view your transformed companion? There's a known issue with trying to view the description of transformed creatures.
Your monstrous companion creature spawns in the arena fine, but it is giving me some errors in the errorlog.
*** Error(s) found in the file "raw/objects/creature_monstrous.txt"
MONSTROUS_COMPANION:Tissue layer not added because no BP found: BY_CATEGORY:EYELID:EYELASH
*** Error(s) finalizing the creature MONSTROUS_COMPANION
MONSTROUS_COMPANION:FEMALE:upper body, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:lower body, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:right front leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left front leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:right front clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left front clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:right rear leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left rear leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:right rear foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left rear clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:middle head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:snout, head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:snout, left head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:snout, middle head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:throat, head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:throat, left head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:throat, middle head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:right dominant facial phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:left dominant facial phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:grasping claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:wickedly curved claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:long sharp claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:viciously sharp claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:cutting claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:first toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:second toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:third toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:monstrous mouth, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:FEMALE:tail, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:upper body, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:lower body, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third right upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third left upper arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third right lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third left lower arm, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third right clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third left clawed hand, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:right front leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left front leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:right front clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left front clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:right rear leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left rear leg, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:right rear foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left rear clawed foot, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third neck, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:middle head, layer 23: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:snout, head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:snout, left head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:snout, middle head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:throat, head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:throat, left head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:throat, middle head, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:right dominant facial phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:left dominant facial phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third right minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third left minor phalange, layer 3: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:grasping claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:wickedly curved claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:long sharp claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:viciously sharp claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:cutting claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:first toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:second toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:third toe-claw, layer 2: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:monstrous mouth, layer 1: Tissue SKIN was not found, using first tissue instead
MONSTROUS_COMPANION:MALE:tail, layer 1: Tissue SKIN was not found, using first tissue instead
I believe the BY_CATEGORY:EYELID:EYELASH error comes from you having these lines:
But your creature has no eyelids.
As for the "Tissue SKIN not found", I looked in your body detail plan, and the skin tissue is based off of a MADNESS_TEMPLATE material, which I don't have. If you have that material and it doesn't have any errors in it, it should work fine for you.
Other than that, I really couldn't say what might be causing your issue.