Tiamat guards the Genji Helm. He absorbs fire, ice, thunder, and poison, so if you want to attack him with
spells, they'd better be FLARE, HOLY, or ULTIMA. Tiamat has high stats, so as you could imagine, he can be
a little tough to takedown.
Tiamat does have a weakness to the Body element, so spells like BLIND, SLOW, and STUN work very well. Use
BLIND and SLOW to pretty much eliminate his physical attack. Even if you manage to do so, Tiamat can still
use his four elemental attacks on your party, but they only cause a little damage. If you've got STUN built
up even a little, you can paralyze him over and over and over again, until you land the final blow. Use
BERSERK and HASTE to give your attacks some extra 'oomph'.