If you look at the wording on Undying (easily found on Flayer of the Hatebound) you'll see that it is basically the same as the wording on the other two creatures you mentioned. So, when their abilities trigger and they enter the battlefield from the graveyard, they trigger Flayer's effect.
December 29, 2014 12:40 a.m.
Assuming you're the owner of all of these cards:
Phytotitan's ability will trigger when Phytotitan dies. The ability will set up a delayed triggered ability that triggers at the beginning of your next upkeep. When the DTA resolves, Phytotitan will return to the battlefield tapped under your control. Flayer of the Hatebound's ability will trigger. When it resolves, Phytotitan will deal 7 damage to target creature or player.
Ashcloud Phoenix's ability will trigger when Ashcloud Phoenix dies. Ashcloud Phoenix will be returned to the battlefield face down (as a 2/2 creature). Flayer of the Hatebound's ability will trigger. When it resolves, the 2/2 creature with no other characteristics (your face-down Ashcloud Phoenix) will deal 2 damage to target creature or player.
December 29, 2014 12:42 a.m.
In short, Flayer of the Hatebound's ability does what it says it does. The ability doesn't care how the other creature was put onto the battlefield from the graveyard. All it cares about is that the creature moved from your graveyard to the battlefield.
December 29, 2014 12:44 a.m.
Alright cool I thought so. But does ash cloud deal 4 damage or 2 since its entering as morph?
December 29, 2014 12:45 a.m.
Ahhh awesome so thorough! I have no more questions
December 29, 2014 12:47 a.m.
Only 2. Flayer of the Hatebound's ability checks the creature's power when the ability resolves. Unless you turn Ashcloud Phoenix face up in response to the ability, it will remain a face-down 2/2 creature, so it will deal 2 damage when Flayer of the Hatebound's ability resolves.