Make images that look like ballpoint pen drawings.
SDXL Version
Keeping "ballpoint pen drawing" in the prompt makes the images more likely to come out as monochrome illustrations. However, you can try removing it to experiment with different looks if you don't mind color and inconsistencies.
This style has a bias for forest background scenes. It's easy to avoid if specify a different background though.
PONY Version
The Pony version can be less consistent so may require tweaking the LoRA weight or prompt between different subjects. I was getting the best results by simply turning up the weight if the result wasn't strong enough.
Adding "lineart", "monochrome", or "flat color" to the prompt can help in some cases. You can also try words like "drawing", "illustration", or "sketch".
Sometimes adding "pen" (like "pen lineart") was helpful, but other times it resulted in the characters holding a pen. I didn't think "ink" improved results in my tests. I didn't see a significant difference from adding "ballpoint" to the prompt