Both Magma Bolts and Eruption are magical damage. See DrP's spreadsheet:
http://forum.shrapnelgames.com/showthread.php?t=36617
Magma Bolts are not AoE, so they are probably blockable by a shield, and may be treated as a missile for the purposes of whether they hit the target (even when they land in the square the target is in).
I'd be surprised if Magma Eruption does not break the mistform every time, if the AoE effect hits the square the titan is in.