Based on the Icy Veins guide:
Tichondrius is basically a one phase encounter with two intermissions. This fight revolves around handling debuffs and getting adds down.
PHASE 1A
Tank attack: Feast of Blood: DoT on tank that increases damage taken, increases the effects of Vampiric Aura, AND spawns 3 Tainted Blood adds that fixate the Feast of Blood target until they are killed.
Debuff: Carrion Plague. 40 second DoT on random players.
Anti-Debuffed player attack: Seeker Swarm. Seeker Swarm is a line attack that travels between the boss and every player with Carrion Plague, hitting every player in its path and applying Carrion Plague to them.
[Heroic only: Debuff: Brand of Argus. Randomly applied to players, persists until detonated, at which point it does moderate raid-wide damage. It can be detonated by standing within 6 yards of a clump of allies. Raid damage is reduced by distance from the detonation.]
Vampiric Aura: healing aura: Any allied targets standing within 3o yards of him to be healed for 400% of the damage dealt by their melee attacks.
Channeled attack: Echoes of the Void: Every 55 seconds. Raid-wide damage which increases in intensity with every tick. 4 fell spires will spawn around the room, each spire will absorb the damage the players behind it would have taken until it is destroyed. The more players behind a pillar, the faster it will be destroyed.
PHASE 1A
Tank the boss slightly off center from his initial spawn point, so that tanks can easily move the Tainted Bloods out of range of his Vampiric Aura.
Players affected by Carrion Plague should move to the SIDE of the room and spread out loosely. It's important that no other players stand between the rebuffed players and the boss, so they don't get hit with Seeker Swarm and get Carrion Plague themselves.
Whenever a tank gets marked with Feast of Blood, tanks should immediately taunt swap and take the Tainted Bloods 30 yards away to escape his Vampiric Aura. DPS should immediately swap to the bloods and kill them fast.
Ranged and Healers who don't have Carrion Plague should loosely spread out in the remaining area. When casts of Brand of Argus go out, we will call out one affected player at a time so that the rest of the ranged can stack on them to detonate the brands one by one. This will give the healers a moment to heal the raid between detonations.
When Tichondrius casts Echoes of the Void, the raid should spread evenly behind the 4 fel spires that emerge. It's important to be evenly spread, as the pillars have invisible health bars and they soak up the damage the players would otherwise have received, so if too many players are behind one pillar it will break quickly and the players will be vulnerable to the Tichondrius' damage.
INTERMISSION
After 130 seconds, Tichondrius will cast Illusionary Night and disappear, leaving the group trapped in a nightmare. Tichondrius will manifest as Carrion Nightmares, which are fel beams that charge for a moment before dealing heavy shadow damage + a 3 second stun.
Phantasmal Bloodfangs will continuously spawn in the nightmare. When they are killed, they drop an Essence of Night which is a raid buff that increases damage, healing and mana regen. The buff persists until the Illusionary Night intermission phase is over and then 30 seconds into the next phase.
INTERMISSION STRATEGY
Stay mobile and alert and out of the fel beams. Kill Phantasmal Bloodfangs so that as many people as possible obtain the Essence of Night buff.
PHASE 1B
Phase Three is the same as Phase One, except that he will begin to summon unique adds. In this phase he'll periodically summon Felsworn Spellguards. They gain speed the longer they are alive. They apply a stacking DoT called Volatile Wound on their targets. When this debuff expires, it will create a void zone called a Nether Zone.
PHASE 1B
The tank which currently affected by Feast of Blood should pick up the Spellguard adds and take them to the back of the room along with the freshly spawned Tainted Bloods. All DPS should prioritize the adds above all else as they do a LOT of tank damage and apply a stacking debuff. If they are not killed fast they'll kill the tank.
INTERMISSION
Same as the first intermission.
PHASE 1C
Phase Three is the same as Phase One, but the boss will summon Sightless Watchers this time. These periodically apply a Burning Soul DoT to a random healer, which does damage and drains Mana. It can be dispelled, but when it is dispelled it does high fire damage to players within 8 yards. The adds will also periodically cast Ring of Shadows which places a ring around a caster and does damage to everyone within 10-20 yards.
PHASE 1C Strategy
Tanks handle the Sightless Watchers just like the adds in Phase Two: grab them and take them to the side. Healers stand near the edges of the ranged stack so they can immediately dispel Burning Soul when it is applied. Ranged either stand within 10 yards of the adds, or over 30 yards away, to avoid the damage from Ring of Shadows.
Tichondrius is basically a one phase encounter with two intermissions. This fight revolves around handling debuffs and getting adds down.
PHASE 1A
Tank attack: Feast of Blood: DoT on tank that increases damage taken, increases the effects of Vampiric Aura, AND spawns 3 Tainted Blood adds that fixate the Feast of Blood target until they are killed.
Debuff: Carrion Plague. 40 second DoT on random players.
Anti-Debuffed player attack: Seeker Swarm. Seeker Swarm is a line attack that travels between the boss and every player with Carrion Plague, hitting every player in its path and applying Carrion Plague to them.
[Heroic only: Debuff: Brand of Argus. Randomly applied to players, persists until detonated, at which point it does moderate raid-wide damage. It can be detonated by standing within 6 yards of a clump of allies. Raid damage is reduced by distance from the detonation.]
Vampiric Aura: healing aura: Any allied targets standing within 3o yards of him to be healed for 400% of the damage dealt by their melee attacks.
Channeled attack: Echoes of the Void: Every 55 seconds. Raid-wide damage which increases in intensity with every tick. 4 fell spires will spawn around the room, each spire will absorb the damage the players behind it would have taken until it is destroyed. The more players behind a pillar, the faster it will be destroyed.
PHASE 1A
Tank the boss slightly off center from his initial spawn point, so that tanks can easily move the Tainted Bloods out of range of his Vampiric Aura.
Players affected by Carrion Plague should move to the SIDE of the room and spread out loosely. It's important that no other players stand between the rebuffed players and the boss, so they don't get hit with Seeker Swarm and get Carrion Plague themselves.
Whenever a tank gets marked with Feast of Blood, tanks should immediately taunt swap and take the Tainted Bloods 30 yards away to escape his Vampiric Aura. DPS should immediately swap to the bloods and kill them fast.
Ranged and Healers who don't have Carrion Plague should loosely spread out in the remaining area. When casts of Brand of Argus go out, we will call out one affected player at a time so that the rest of the ranged can stack on them to detonate the brands one by one. This will give the healers a moment to heal the raid between detonations.
When Tichondrius casts Echoes of the Void, the raid should spread evenly behind the 4 fel spires that emerge. It's important to be evenly spread, as the pillars have invisible health bars and they soak up the damage the players would otherwise have received, so if too many players are behind one pillar it will break quickly and the players will be vulnerable to the Tichondrius' damage.
INTERMISSION
After 130 seconds, Tichondrius will cast Illusionary Night and disappear, leaving the group trapped in a nightmare. Tichondrius will manifest as Carrion Nightmares, which are fel beams that charge for a moment before dealing heavy shadow damage + a 3 second stun.
Phantasmal Bloodfangs will continuously spawn in the nightmare. When they are killed, they drop an Essence of Night which is a raid buff that increases damage, healing and mana regen. The buff persists until the Illusionary Night intermission phase is over and then 30 seconds into the next phase.
INTERMISSION STRATEGY
Stay mobile and alert and out of the fel beams. Kill Phantasmal Bloodfangs so that as many people as possible obtain the Essence of Night buff.
PHASE 1B
Phase Three is the same as Phase One, except that he will begin to summon unique adds. In this phase he'll periodically summon Felsworn Spellguards. They gain speed the longer they are alive. They apply a stacking DoT called Volatile Wound on their targets. When this debuff expires, it will create a void zone called a Nether Zone.
PHASE 1B
The tank which currently affected by Feast of Blood should pick up the Spellguard adds and take them to the back of the room along with the freshly spawned Tainted Bloods. All DPS should prioritize the adds above all else as they do a LOT of tank damage and apply a stacking debuff. If they are not killed fast they'll kill the tank.
INTERMISSION
Same as the first intermission.
PHASE 1C
Phase Three is the same as Phase One, but the boss will summon Sightless Watchers this time. These periodically apply a Burning Soul DoT to a random healer, which does damage and drains Mana. It can be dispelled, but when it is dispelled it does high fire damage to players within 8 yards. The adds will also periodically cast Ring of Shadows which places a ring around a caster and does damage to everyone within 10-20 yards.
PHASE 1C Strategy
Tanks handle the Sightless Watchers just like the adds in Phase Two: grab them and take them to the side. Healers stand near the edges of the ranged stack so they can immediately dispel Burning Soul when it is applied. Ranged either stand within 10 yards of the adds, or over 30 yards away, to avoid the damage from Ring of Shadows.