So I want to install the silverfish mod and all I need to know is that is this the correct download link:viewtopic.php?t=26283&p=378508 . And how do I install a mod onto S.M.B.X and which version do I use?
It's not exactly called a mod, but an "NPC pack". These are installed into separate levels, not into the game itself. Download and unpack it in the directory of the level you want to use it in, along with the custom graphics and stuff
The recommended version is SMBX2 beta 4 because it's the most recent official version.