Celeste

This heart is on the outside of the level 2 before you enter it. You will have to have assist mode on and infinite boost to be able to boost high enough, but keep going up from the campsite and to the right until you hit a ledge with a heart on it. Bingo!

*Update thanks to platinumpwnzor*

The legit way is to abuse the fact that your dash refreshes on every screen change...

This is definitely the easiest Crystal Heart in the game to collect. You'll abuse the fact that switching screens refills your dash and allows us to dash back and forth between screens, both from side to side and up and down.

Find where the first screen wrap is and jump and dash up-right into it, causing the screen to change to the next zone. Your dash will refill, so dash up-left this time to change screens back to the previous zone. Repeat this until you can climb up the wall overhead. Climb it through the next two zones to end up at a roof that you can't climb through. Jump and dash left to get some distance, then fall through the screen change to end up one zone down, where you can now dash up-left to re-enter the zone above with a fresh dash. Repeat that until you can dash up and grab onto the wall overhead. Climb from there to find the crystal heart waiting patiently for you. Dash into it and enjoy your achievement.

Timestamp: 24:53