Some level tiles are empty!

If you have a random empty tile in the middle of your level, that's because Sibyl made a mistake or failed to find a tile in your template that could go there. To correct a failed tile, use the erase brush (right mouse button) to delete the area around it. Then press space to fill it in. If another failed tile pops up, try erasing a larger area to get rid of it.

If failed tiles are happening often, your template may be missing some important tile combinations. Take a look at Sibyl's failures and check the tiles around them. Then make sure add some tile combinations to cover those failures in the future. If your template is too unwieldy, try simplifying it instead.

Level generation is taking too long!

The time Sibyl takes to generate a level depends on your template's number of individual tiles and tile combinations, as well as level size and edge / corner detection. Because Sibyl has to do so much work to generate each level, you may prefer to use Fast Generation for more complex templates and let Sibyl do it's thing in the background. 

Editing levels is also faster than generating them from scratch. If your template takes a while to generate and you only have a few things you'd like to change in its most recent level, try editing those parts instead. If that doesn't work for you, you could also simplify your template to reduce Sibyl's workload. 

Level outputs are too rigid!

The flexibility of Sibyl's levels depends on the flexibility of your template. You may have a lot of unique tiles in your template, which each force unique (and therefore rigid) tile combinations. Don't be afraid to copy-paste tiles across your template to give them more possibilities. Applies to each direction separately, so feel free to mix and match adjacent combinations.

Another quick solution may be to simply your template's tile variations (like using only one ground, wall, and sky tile) and then slowly add variation back in. You could also try enabling 16x16 tiles if your tileset is 32x32 or larger, which will allow for more freedom at the cost of structure. 

Otherwise, make sure to avoid "noise" in your template, such as inconsistent particles, bloom, rendered lighting, or misplaced pixels. Even a pixel of difference will tell Sibyl to recognize two tiles as entirely separate, and give them separate rules, so try to keep your tiles consistent. Keep tile variations (such as alternate grass tiles) isolated and surrounded by the tile they're meant to sometimes replace.