I've spent the past hour trying to do this simple puzzle.
Apparently you're meant to have death protection on while fighting Jormungandr so that you can still live. After getting Death Protection confused with the Wolf Icon (it's the person with a heart), I figured out what was going wrong. Death Protection is being removed when I level up.

As soon as I kill the first Goblin (Fire, Super Punch x2), I level up and I lose the Death Protection.


Right so I needed to make sure I could heal in between using an Glygh and healing potion. That's why I couldn't keep holding the Death Protection.

Solved it... Thanks for your help.

It is possible to win -
you start the puzzle with 10 hit points.
each time you hit the goblin you lose 6 hit points
so after Fire Super Punch x2 you have used 12 hp and therefore used the Death Protection.

so you have to use a health portion before punching the last time.

I think the problem is that the readout can fool you:
Right before the last " Super Punch" It says 4/10 - Placed where your life will be drained to.
The numbers is because you have used 6 hp and have 4 left.
Looking closer the coloring show that you will be left with 1 hp. Implying the usage of Death Protection.
It is also shown with a small number (1) inside a black box over the health line.
This i failed to notice at first. So I assume it might be the same for you.