The patch is failing because the other patches that you have previously applied have shifted the code around sufficiently to defeat patch's attempts to apply the change, even with an offset (as can be seen in those hunks that did succeed).
If you open `dwm.c.rej` you will see the failed hunks, then it is just a matter of hand patching them in to `dwm.c`.
For each failed hunk, search in `dwm.c` for the original code (the lines that begin with a `-` in `dwm.c.rej`) and replace them with the patched code (those lines beginning with a `+`). If dwm recompiles without error, you have successfully patched in transparency.