Alas, when I found this secondhand Playmates 1988 Teenage Mutant Ninja Turtles Splinter action figure, for fifty cents, at a thrift store, he was naked, except for his black belt. Truth be told, the thrift store actually had two copies of this Splinter figure the day that I bought mine, which was rather unusual. Only one had its belt though, so, I obviously bought the more complete version (and, no, I didn't want twins), as they were both the same price anyway.
An unclad Splinter isn't something I enjoy seeing, so, I decided to make him a replacement robe:
The first thing that I did was search for a photo of the original garment, laid out flat, so that I could copy the pattern. The person who was selling this item was also kind enough to list its width, 4.5" (11.4 cm), which was very helpful for sizing purposes.
Next, I scaled that reference image, on my computer screen, until it was the exact dimensions that I wanted. I then placed a piece of tracing paper onto my moniter and carefully traced the outline and neck hole of the garment.
After that, I transferred the tracing onto a piece of sturdier paper, a page from a lined notebook, and cut it out to use as my pattern.
I affixed the pattern to an old, red T-shirt, with transparent tape, so that it wouldn't move around on me while I was cutting it out. The fabric used for the original robe was more of a magenta color, but, I don't have any clothing of that hue, and I wasn't going to go out and buy something just for a quick little project like this, so, I made do with what was on hand. Splinter is often depicted wearing a crimson robe anyway, so, it's not like it looks out of place on him.
Finally, I cut the robe out with a pair of very fine, sharp scissors (fingernail trimming ones to be exact). Note: to cut out the "T" opening in the neck, fold the fabric in half, along the center of the "T".
And voila, here it is. If I had to do it all over again, I'd make it just a smidge bigger/longer, but, all-in-all, I think it came out very well.