Guild Wars 2

There are quite a few threads on this already, including what was meant to be a collaboration of issues regarding the Elementalist.
It seems to be the general consensus that the Mist Form ability (along with other invulnerability effects) is a bit iffy in situations where conditions are already applied to you.
Certainly, this will be either fixed, or clarified, at some point.

My experience with invulnerability (through Mist Form and Obsidian Flesh) is generally that fall damage, certain environmental damage and already-applied damage-over-time conditions such as poison, bleed and burning, all ignore the effect and still do damage.

zetherin.8372:

I may be alone in this but when I play my ele, I put down conjured weapons specifically for other people to use. And when some random person walks up and takes the hammer I put down for them, and then charges into battle with it.. it just makes me happy.

I love throwing down the Greatsword for that very reason. It’s fairly powerful, too.

I’m personally running a Scepter/Focus spec which centers around bleeds, and I find that while Dagger OH would give extra bleed with Churning Earth, I absolutely adore the extra survivability provided by Magnetic Wave and Obsidian Flesh.

MajorMelchett.6042:

Mist Form: It states in the tooltip that you invulnerable for the duration of the spell, but I have died countless times to DoT damage during this form, if this is intended, then the tooltip needs to be changed to state that I think.

This also holds true for Obsidian Flesh (Earth Attunement, 5th Focus ability).
Additionally, fall damage and other sorts of instant-kill environmental damage seem to ignore the invulnerability effect.