I just got the Talaria Attachment, allowing me to dash. However, I have not found anything I can usefully do with it. If I maintained my dash momentum while jumping, I could clear the high barrier in the room below the one where I found the Talaria Attachment. That's exactly what appears to happen in this video at 13 minutes 34 seconds: But, if I jump while dashing, I lose my horizontal speed, so the dash doesn't allow me to jump any farther than I could without it. Am I missing an item that would give me this ability, or is this a bug? If it's relevant, I'm playing on Mac OS with keyboard controls.
Sorry, this turns out to be my error. When I assigned keyboard controls, I accidentally set the same key for jump and backdash. I moved them to separate keys and I can now do dashing jumps. Feature request: have the key mapper prevent silly people like me assigning multiple actions to the same button.