Klaus said:
But my point is, having hp and AC doesn't make it a creature automatically.
True, but almost anything the players can interact with in a physical sense (ie: beat to death with swords or magic) has hp and AC. As Hypersmurf mentions, it is the sentence "
You conjure a Large, quasi-real, horselike creature" that we believe gives this thing creature status.
And the Fiendish Dire Weasel was summoned by a Conjuration (Summoning) effect that points you to the stats of the creature. No such thing for Phantom Steed, which is an Illusion (Shadow) spell.
Check again.
Phantom steed is conjuration (creation).
The lower level
Mount spell, which does summon a real horse is a conjuration (summoning) spell. As one subschool (summoning) brings forth a real, living creature, it would suggest that
phantom steed, a (creation) spell, doesn't summon a real thing, but creates something that wasn't there before.
I don't have access to
Wyvern's Watch so I can't comment on the elements of that spell.
Sepia Snake Sigil is a conjuration (creation) [force]. However, unlike
Phantom Steed, the snake sigil can not physically be interacted with like the steed can be. Using that spell for comparison is difficult.
Mage's Faithful Hound is also a conjuration (creation) spell, but again, it provides no physical body (no AC or hp). Its spell effect is to create a force that watches, barks, and attacks. Nothing else.
Phantom Steed's spell effect is to conjure (create) something that is physically like a horse, but actually has a physical body. It has a body (it can be attacked), but being
quasi-real is not really alive, and thus has no metabolism... fitting the requirements for having no Con score.
And a creature with no Con score can run without fatigue... unless otherwise stated.