This is based on the Lego(tm) original "Ultimate Dume" model - I make no claim whatsoever to that - he's Lego's design!
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I don't know about you, but I find Ultimate Dume, well, a bit less than "Ultimate". He has a tendency to fall over, looks a bit spindly, and is distinctly limp-shouldered, being completely unable to hold his arms out in front of him for more than a few seconds... (Maybe my new-style ball socket parts aren't quite right?)

Well, here are a few mods to take care of these matters. The leg and arm ones are fairly minimal and practical; the "cosmetic" ones are a matter of taste.  They can all be done at once, using only parts withing the Ultimate Dume set - no rootling in your spares box required.


Quantities for each sub-assembly: you'll need two of each except the neck and torso mods
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Leg stabiliser:
1x 32013 PearlLtGray Technic Angle Connector #1 
1x  3749 Tan Technic Axle Pin
1x 32002 DkStone Technic Pin 3/4  
1x 32580 FlatSilver Technic Axle Flexible 7 

Make sub-assembly from parts. Attach to socket joint above back of knee and 2x4 liftarm on heel.

Corrects tendency to fall over, at the expense of a bit of flexibility.
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Arm stabiliser:
1x  6587 DkStone Technic Axle 3 with Stud 
1x 4265c MdStone Technic Bush 1/2 Smooth 
1x   x71 White Rubber Belt Small 

Assemble bush onto axle, an insert into shoulder. Dismantle arm sufficiently to loop belt around its central axle. Re-assemble arm, then hook belt around bush.

Allows Ultimate Dume to hold his arms out more-or-less horizontally; you may need to adjust the position of the belt on the arm for maximum "pull".
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Wing hook:
1x 32551 FlatSilver Technic Hook with Axle 
1x 32014 Black Technic Angle Connector #6 
1x  6587 DkStone Technic Axle 3 with Stud 
1x 32062 Black Technic Axle 2 Notched 
2x 4265c MdStone Technic Bush 1/2 Smooth 
alt instead of Black #6 (better colour, worse hook position):
1x 924 PearlLtGray Technic Angle Connector #4 

Make sub-assembly as shown, but leave off second bush on the end of the Axle 3. Remove wing from socket joint, and attach sub-assembly to socket joint. Re-assemble socket joint to wing - Axle 3 goes through liftarm and is retained by the unused bush.

Purely cosmetic.
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Neck mod.:
4x  6587 DkStone Technic Axle 3 with Stud
2x 41668 Black Technic Connector Block 2 x 3 x 5 with Ball Socket 
2x  x346 TrOrange Technic Bionicle 1 x 3 Tooth with Axlehole 
1x 32184 White Technic Axle Joiner Perpendicular 3L  

Make sub-assembly as shown, but leave out the two Axle 3s in the Bohrok foot heels. Drop into gap in front of neck, and secure with Axle 3s.

Cosmetic, but hides the rather duff "turkey neck" without unduly restricting head movement.
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Torso mod:
1x 45425 FlatSilver Technic Bionicle Rahkshi Staff of Power 
1x 44036 FlatSilver Technic Bionicle Toa Nuva Claw 
1x 3673 MdStone Technic Pin 
1x 6558 Black Technic Pin Long with Friction

Remove triangular connector block/angle connector #1 sub-assembly from chest, dismantle and replace connector block only, leaving you with 1x 32013 PearlLtGray Technic Angle Connector #1. Make sub-assembly as shown, including the Angle connector #1. Note the relative positions of the long and standard pins (more easily seen on the "in-situ" picture). Attach to torso.

Purely cosmetic.