Where the Wild Things Are

Just thought I would add this little tidbit to help people get this. There is a part in the stage "Below The Roots" right after you do the 3 tree stumps part. You will climb up and get a checkpoint. If you look over to your left you will see 3 exploding bugs and 1 green bug. What I did was just killed these 4 bugs and reloaded my checkpoint. It's really quick and gives you alot of experience in a short amount of time. I gathered my last 2 hearts in about 15-20 minutes doing this. Hope it helps.

I believe I may have stumbled upon a better spot to obtain this. First of all, I would suggest first getting all of the collectibles, as you will gain XP while doing so, therefore getting you that much closer.

Collecting all of the geodes makes the rest of the collectibles laughably easy because it gives you the cheat that shows you where all the others are. The next goal is the turtles. This gives you the "kill enemies in one hit" cheat.

After you have the one hit cheat, enable it and play the level "seasick." Right near the start of the level, after you climb up a bit, you will be thrown by the wild thing and hit a firefly hive. The game gives you a checkpoint here. You will be attacked by a large group of fireflies. Make quick work of them (due to the cheat). Now throw a rock at the hive on the mountain side. The wild thing will follow suit and destroy it, releasing another large group of enemies. After you kill them, reload the checkpoint. Rinse and repeat as needed. These two groups will net you massive amounts of XP. I finished my last heart only reloading checkpoint one time. I cant imagine filling your last heart or two in full would take more than a couple minutes.

Edit: Dan Solo 88 brought up that if you have the invulnerable cheat active you will not progress towards the next heart, so make sure that cheat is turned off when working towards this.