I had him, spawn on the platforms, where the 3 steamwork menders are, and also had him spawn as a roamer, between Oozes, as I was looking for the GearmarshaL
Casts Freezing Mist (makes sense for a firemarshal, right?) http://lucy.allakhazam.com/spell.html?id=7939&source=Live
Max hit against an 80 monk with 3.4k AC, 17% shielding, max defensives was 3013. his DPS against the same monk was 837. (please note, he was unslowed) Runs faster then regular trash, which helps with pulling, until he snares you with Freezing Mist. Dropped Fire warning.
*edit* A necro who came with me to kill this guy informed me that this mob is nearly 100% magic resistant, but that other spells landed just fine.
Max hit on a 80 sk with max shielding and 4.1k ac was 4627 average was 2.5k-3k. Resists almost everything including chanter slow and cripple and sk taps