The Secrets of Phoenix

Coming fresh from the lands of DotA Allstars to the fields of battle, Phoenix is reborn into Dota 2. Armed with Icarus Dive, Fire Spirits, Sun Ray and Supernova, ask yourself how well you're prepared to face such a foe.

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Q: Icarus Dive

Health cost is HP removal-type, meaning magic resistance / going ethereal doesn't affect it. Magic immunity does not prevent the health cost either. It also means you can use any items like Urn of Shadow, Salve or Clarity without breaking them by casting Icarus Dive.
Walking on the fire trail left by Icarus Dive does not inflict the debuff, only contact with Phoenix during Dive will.
Debuff can be removed by going magic immune / using purge. Dive doesn't affect magic immune units.
Phoenix can freely attack / cast spells / use items during Icarus Dive.
Always arc from left to right. There is an area in the middle that Icarus Dive doesn't touch.

Dive will ignore terrain & trap-type spells such as Power Cogs (doesn't trigger zap) or Pounce. Dive will also destroy trees.
Dive does not grant flying vision.
Dive does not disjoint projectiles & spells.
Icarus Dive can be stopped by most hard CC such as stun, hex, sleep or Disruption. Mini-stuns cancel Icarus Dive too. Vacuum stops Icarus Dive, but does not pull Phoenix.

Icarus Dive is not cancelled by the following:

Eul's Cyclone / Invoker's Tornado. Phoenix takes damage from Invoker's Tornado but is otherwise unaffected.
Entangle / Ensnare type spells (with the exception of Frostbite which mini-stuns before snaring).
Chronosphere. Phoenix can fly through ally / enemy Chronosphere without any issue. However, you can't fly over Enigma's Black Hole.
Telekinesis (probably a bug).
Pudge's Meat Hook (still take damage but won't be pulled)
Taunts & Silence. These will prevent Phoenix from using Stop Icarus Dive, and taunts will still make Phoenix come back to attack the target after Dive ends.

Special interaction between items & Icarus Dive:

Force Staff will not have any effect (still goes on cooldown).
Blink Dagger & Manta Style immediately stop Icarus Dive.
Going invisible (Shadow Blade) will make both Phoenix & the burning trail invisible.
Shiva's Guard AoE follows Phoenix during Dive.
Phoenix can start TP during Icarus Dive.

W: Fire Spirits

HP cost follow the same rules as Icarus Dive.
Creates 4 Fire spirits. After 16 seconds, all spirits that haven't been used are wasted.
Cooldown starts when Spirits are created, not when the last spirit is thrown.
Debuff does not stack. Throwing multiple Fire spirits only refresh the duration.
If chained perfectly, can deal 1200 magic damage at max level (300 per spirit).
Debuff can be purged / removed by going magic immune. Does not affect magic immune units.
Inconsistencies: Dota 2 Fire Spirits don't grant vision / Dota 1 each spirit has 300 vision range.

E: Sun Ray

HP costs is not paid upfront but updated every 0.2 sec at a rate of 6% HP / sec. This means a fully channeled Sun Ray (6 sec) would be like paying 31% of your current HP and not 36% (geometric sequence with a 0.94 ratio). This cost is increased if Phoenix is healed during the channeling / decreased if Phoenix takes damage during the channeling.
Damage scales up to twice the initial damage, meaning it increases by 20% every second. At max level, a fully channeled Sun Ray deals 270 + 36% of the enemy's max HP in pure damage.
Sun Ray also heals for half this amount. At max level, Sun Ray can potentially heal 135 + 18% of the ally's max HP.
Magic immune enemies are not affected by Sun Ray, but magic immune allies are still healed.
Sun Ray grants vision in a very small AoE around the beam.
By default Phoenix can't move during Sun Ray, and turns at a reduced turn rate of approximately 30 degree / second.
Toggle movement makes Phoenix fly in the direction of the beam at a fixed 250 movement speed. Speed modifiers such as slows, haste or even items do not affect this value (though their effects resume normally after Sun Ray ends).
Similar to Icarus Dive, Toggle Movement grants Phoenix flying movement and ignore terrain & trap-type spells like Power Cogs. It will not grant Phoenix flying vision, and will also make Phoenix destroy trees in his path.
Ensnare / Entangle type spells still have no effect. You can even activate Toggle Movement after being snared to fly away. As usual Frostbite is the exception and will mini-stun you out of Sun Ray.
Unlike Icarus Dive, Silence immediately ends Sun Ray. Enemy cyclone / tornado also cancels Sun Ray.

Special interaction between items & Sun Ray:

Using Eul's on yourself (enemy Eul will simply cancel Sun Ray) will not stop Sun Ray. Phoenix will still lose HP and although the beam graphically shoots forward, in reality it spins with Phoenix .
Blink Dagger is disabled during Sun Ray
Force Staff works normally
Invisibility glitches Sun Ray's visuals. You can still see the beam but it won't update any rotation / movement, effectively creating a false beam. This false beam disappears when Sun Ray ends.
Remember you can use items / spells during Sun Ray without cancelling it.

R: Supernova

Refreshes Phoenix's other spells cooldown upon completion, but not his items cooldown (unlike Rearm / Refresher Orb).
Magic immunity blocks the damage, but not the stun.
Phoenix is hidden inside the sun during Supernova (much like Brewmaster in his Earth Brewling), meaning any aura he is carrying is still active. Radiance for example will increase the total damage output of Supernova by 300 magic damage (but it's still a bad item on Phoenix, so don't build it please).
The sun is immune to all spells (allies / enemies) and can only be destroyed from a set amount of hero attacks. Creeps & towers will still attempt to attack it but will deal no damage.
Similarly, illusions will also deal no damage. Meepo's clones are considered as real heroes for that purpose (probably the only time they can boast to be real heroes).
If you feel troll, you can start denying an ally sun once it drops below 50% HP. A denied sun will grant no XP / Gold for the enemy though.
Supernova does not stun if it ends prematurely.
If Chen uses Test of Faith before Phoenix goes into Supernova, if the sun survives Phoenix will re-appear at base. This technique does not work with Disruptor's Glimpse, Phoenix will still appear under the sun.
If Phoenix uses Blademail before going into Supernova, killing the sun while Phoenix still has Blademail activated will deal a huge amount of damage to the killer, equal to the HP Phoenix had when he used Supernova.
Using Supernova right after Force Staff will create the sun immediately, but Phoenix will reappear at the end of Force Staff location when Supernova ends.