Thanks for the feedback! There's two (three?) frames of animation when transiting from running state to sliding state, if that's what you mean, but the collision box shrinks instantly. Do you think the transition should rather be instantaneous? As for the powerups - it's a part of strategy whether to pick them up or not, especially the confusion one. It shouldn't slow you down more than to 5 m/s, otherwise it's a bug. Doing double jump should let you clear an obstacle even at that speed.
Now that, my friend, is a bug, which happens after you die once - the game should reset your invulnerability to false in case you had one, but it sets it to true instead - I forgot to change it after testing with god mode on... Thanks for discovering it! I'll push a new build soon.
Normally, the sword can only break through boxes and wooden doors. In a situation like in the picture, you just have to jump a bit earlier to manage to slide in time. I will make the slide transition a bit faster as well.