Random thing I made for myself and turned out well enough to publish.
Pony instructions:
works well at around 0.7 strength
Use keyword 'mask' to add the mask.
SD 1.5 instructions:
Can be used for both for either male or female (might need to throw in a few extra simple tags)
I find it's best used at 0.5-0.7.
To use the word mask and unmasked to get or remove the mask, can work better if you put the opposite in the negative prompt.
If you enjoy my work please leave a like or a review. Pics of your work are also appreciated :)