These large flightless, featherless birds appear as heavy ostriches.
Beside each of their two dully-glowing red eyes is a small duct from
which the beast can project a small fireball which does 1-6 hit points
of damage. The beast can project these fireballs at the rate of two per
hour (one from each duct) with accuracy as a +4 longbow, a
maximum range of 50' and a burst radius of 10'.

In addition, the giant strider can attack to its front or flank with a bite
for 1-8 HP of damage or deliver a kick to its rear for 1-10 HP of damage.
It cannot, however, co-ordinate both attacks
simultaneously in the same melee round and will generally launch its
attack in the direction from which it was last hit.

These birds are immune to fire, magical or otherwise, and in fact their bodies
have adapted to derive sustenance from warmth; consequently
they are most at home in desert and volcanic regions. Intense heat,
flames, fireballs and so on act as a [cure light wounds] spell on them
once every three rounds. As a result, giant striders are often found
wading in lava-beds or standing in the flames of a forest fire (it is
possible that the phoenix legend derived from such a sight).

Conversely, cold spells and the like do an additional 2-7 HP of damage
and water (if drunk) is poison to them. Even if a cold liquid
is thrown over their bodies, they will take some damage (at the
discretion of the DM according to the circumstances, but normally
1-2 HP damage).

These creatures are used as steeds by the firenewts. They are generally
fearless and never check morale.
 

    by Albie Fiore