We're all familiar with the startpos switcher to practice certain parts of a level, but what if we can make it even better?
My suggestion is creating this feature:
In a startpos level, select a starting point, let's take 0%. Let's also say there's a startpos every 10%.
A run starts from the start point. If you die at, for example 24%, you'll respawn at 20% (the last passed startpos). If you then do a run from 20 to 51, you respawn again at 50%.
It's a sort of 'checkpoint based' practice mode that, I believe, will be really useful for practice. Also, if you do a run from 0 and end up getting 100% without dying I think it should count as a full run.