Vantablack Vesper

It opens by showing off its wings. Its gauge fills and it throws the moves below on its own clocks, while the three parties hit back.

• Void Pulse
  The seam opens and the dark rolls out in a ring. The back row gets the leftovers.

  A magic hit on every member of every party (the back row takes 60% of it), and each hero it lands on is left with 1 Void Rot. It hits 35% harder while the Carapace holds.

  first at 0:09 into the fightevery 16 s2.5 s wind-up
• Unblinking Gaze
  The lower eye picks a favourite. It's you. Sorry.

  Picks the member with the least share of HP left and Marks it: it takes 60% more damage for 6 s.

  first at 0:14 into the fightevery 20 s0.8 s wind-up
• Gaze Lance
  A pillar of light from something made of none. Bit hypocritical.

  A big magic hit on the Marked member, landing a moment after the mark.

  lands 2 s later
• Void Carapace
  Grows crystal plates over its chest and hits harder behind them. Unmake is the tin opener.

  Crystal plates over its chest: a shield worth 6% of its max HP. Burn through it, or dispel it with Unmake. It falls away at the phase change.

  first at 0:02 into the fightevery 1:251 s wind-up
• Lights OutNuke · Brace!
  The eyes go dark for a long, long breath. Brace yourselves.

  The phase's big one: a magic hit on every member of every party. Magic defence, guards and shields soften it, and a well-timed Brace! softens it further.

  first at 0:30 into the phaseevery 2:054 s warning

Below two thirds it changes: the shield goes, the shards come, and it gets chatty with the casters.

• Void PulseCarries on, a little quicker.
  every 14 s2.5 s wind-up
• Unblinking GazeCarries on.
  every 20 s0.8 s wind-up
• Gaze LanceCarries on.
  lands 2 s later
• Shard Rain
  The wings crack and the bits get up on their own. Each one makes the boss feel very supported.

  The wings crack at 66% of its HP, and again at 50%: 3 Void Shards get up (at most 4 stand at once), each with 3.5% of the boss's max HP. Each living shard makes the boss hit 15% harder, and while any shard lives the boss takes 50% less damage. Area attacks clear them fast.

• Shard Siphon
  A shard sips your mana through a very small straw and makes healing taste of nothing.

  A shard's own attack: a magic hit that burns 15 mana and cuts the healing its target takes by 50% for 8 s.

• Hush
  The seam closes and so do two of your casters' mouths.

  Silences two random casters (anyone with a skill or a magic attack) for two actions. A dodge evades it.

  first at 0:04 into the phaseevery 18 s0.9 s wind-up
• Dark NoonNuke · Brace!
  Midday, minus the day. Shields up, guards up, snacks down.

  The same trick, harder than the last: a magic hit on every member of every party, with a wind-up to Brace! in.

  first at 0:20 into the phaseevery 2:404 s warning

Below a third it stops pretending. The rot stacks faster, the wings turn to mirrors, and the whole sky leans in.

• Totality

  The change itself: the boss is 25% faster for the rest of the fight.

• Void PulseCarries on, quicker still, and each hit now leaves 2 Void Rot.
  every 11 s2.5 s wind-up
• Unblinking GazeCarries on.
  every 20 s0.8 s wind-up
• Gaze LanceCarries on.
  lands 2 s later
• HushCarries on.
  every 18 s0.9 s wind-up
• Mirror Wings
  The wings fold into a mirror. Hit it and you'll mostly be hitting yourself.

  The wings fold into a mirror for 8 s: 40% of the physical damage dealt to the boss comes back at whoever dealt it. Unmake lifts it.

  first at 0:06 into the phaseevery 30 s1.5 s wind-up
• The EclipseNuke · Brace!
  The whole sky leans in. If you were going to brace, now's lovely.

  The same trick, harder than the last: a magic hit on every member of every party, with a wind-up to Brace! in.

  first at 0:15 into the phaseevery 3:354.5 s warning