5 Instances?

[ShadowHarlequin]

Custom shapes and custom waves each have variables which allow the author to change the shape, size, color, and location on screen, among other things. Shapes and custom waves each have internal per_frame code that affects these variables similarly to how per_frame equations affect the entire preset. Custom shapes and waves equations are included in MilkDrop version 1.04 and later.[2] While initially MilkDrop allowed 4 custom shapes and waves, the latest version of the MilkDrop beta allows up to 5 custom shapes and 5 custom waves to be utilized per preset

I have Winamp 5.5 and theres still only 4 instances listed in the editor?

[redi jedi]

5 were in the 1.05beta versions I was building, milkdrop 2.0 is based on 1.04d so none of the changes in my beta are included, although some are made obsolete.

you can do instances of a shape now though, so you have the same shape multiple times with a variable for which instance it is, that's close enough i guess and provides other abilities too.

[ShadowHarlequin]

is that using the num_inst variable?

[Flexi]

num_inst gives the number of how many instances are set manually and instance gives the number for each of them.

maybe use it like this:
sample = instance/num_inst;