Hello, this my first guide on steam and I hope you enjoy it.

Since those two achievements don't have to be done in a specific stage, you can do them wherever you feel like. I felt it was the easiest to do them in Stage 8, because of the nearby checkpoints.
So if you mess up you can try again pretty fast.

This is right after the first checkpoint in the stage.
As soon as you start walking over the springboards the bouncing hearts start to spawn from the presents. Since the game let's you jump only at minimal height when standing on a springboard you have to wait until the bouncing heart almost hits you before jumping. If you jump too soon you will already have landed before the heart hits you resulting in a death.

This is after the second checkpoint in the stage.
You have to pick up the flower on the right, which will set you on fire. Afterwards you have to jump in that pit with the cupcakes. While on fire you kill every enemy on contact but you have to keep moving, otherwise you'll die. When the cupcakes are killed they respawn really quick from the presents, so just keep running in the pit. Watch out for the venom spitting plant on the left because if the venom hits you it puts out the fire. After you killed 30 cupcakes the achievement should pop up.