oh,also i had an idea for a hub puzzle,its about entering levels and exiting them to go to the same place but your stone keys reset,heres what im thinking (edit:you have 12 stone keys) :
| [other stuff above] | wall | ||||
| wall | wall | wall | wall | wall | |
| 9 stone (2x2) | 2 stone (1x2) | level | |||
| wall | wall | wall | 9 stone (1x5) | wall | wall |
| wall | [starting area below] | wall |