This is my very first custom figure, and now I feel like I've worked up to a point that I'm happy to share.
As the figure's original head is slightly on the small side, it looks a bit awkward when it is displayed with other figures in the same series, so I bought a custom head from my friend Tumtist (a realmr who submitted another custom AK batman in here before), and I modify on top of his custom head.
The eye brow, nose, and mouth are re-sculpted, and especially the mouth was the most time consuming part as a mistake would look very obvious.
I've volumed up his mouth and chin, making him look grumpier and give more quality to his facial muscles.

Apart from the head, I also customized his cape. I cut the original cape out, and drill 2 holes under his back's armor, so that I can attach the cape nicely.
I used Lycra fabric to make the cape, and wired it with some craft wires.

I'm very happy with this custom, as Batman looks great among my other AK figures now.