This was a relatively simple custom. The DCUC Black Manta is an extremely nice and versatile base figure. His head pops off easily and the neck brace isn't even glued in place. The only thing to remove is the backpack, which comes off easy as pie with a little heating.
The head was from a nameless 6 inch soldier figure. I dremmeled his hair and features down and fine sanded the head smooth. The visor is a piece of plastic glued in place. The ear pieces are from the belt clips on some Iron Grenadier figures. The pouches on his arms and legs are from various ChapMei figures. The belt is actually from the first 25th Anniversary box set Snake Eyes figure! The sword and knife were custom made from plastic. The grey straps and holsters/sheathes are pleather. The guns from the nameless 6 inch soldier figures.
I wanted a nice base for him, so I used the base from a Fantastic Four: Rise of the Silver Surfer Doctor Doom figure with new foot pags. I weighted the base, added a new bottom, and decoupaged a GI JOE logo I trimmed from an old action figure catalog included with a random VvV figure (I know you JOE collectors all have TONS of these).
And that's that! The dynamic base figure did the work for me-- DCUC figures pose so well it's staggering!