I first noticed this on level 3 where jumping up the slope rather than running up it seemed to give me more time before having to duck under the fireball. I tested it on level 1 and sure enough, I saved about 0.2 seconds. So, PSA: you can save several tenths of a second for free by jumping up slopes. The main levels where this is relevant are 1 and 3, where combined you can save nearly half a second (in 100% runs).

Conversely, running down slopes seems to be faster than jumping down them. This has a much smaller effect — a few hundredths rather than tenths — and is relevant in levels 1, 2 and 3. I used this to save another couple frames on level 1.

nice to know that !