Week 11 Session: A Boss Is a Puzzle With a Health Bar

The boss script as a decision tree — state, telegraphs and thresholds, read off one Final Fantasy X fight and its two solutions

3 May 2027

A boss is where every week so far gets pointed at one encounter, and the script is the document doing the aiming.

if hp <= 10000 and not hasted:  cast Haste
if last_action == Inhale:       Poison Breath
if distance == close:           Claw, Claw, then Inhale
if distance == far:             Photon Spray or Swooping Scythe
if target casts Slow:           counter with Haste

That’s most of Evrae, the airship boss in Final Fantasy X, as a script. 32,000 HP, halves every element, and one state variable that the player controls: distance.

Reading the tree#

Cid appears in the turn list like anyone else. Tidus or Rikku can queue a command telling him to close in or pull back, and that single variable selects which half of the script runs.

Close, Evrae claws for around 1200 to one character, petrifies, and every third turn inhales — and the turn after an Inhale it breathes poison for about 1500 to everybody. Far, it throws Photon Spray for a scatter of small hits, or Swooping Scythe for 700 to 800 across the party, which drags it back into close range by itself.

Three things are doing all the work here, and they’re the three things in every boss script worth studying:

• State the player can change — distance, and nothing else.
• A telegraph — the Inhale, which announces the one attack big enough to matter a full turn before it lands.
• Thresholds — 10,000 HP, where it hastes itself and the fight speeds up.

The intended solution and the other one#

Intended: watch for the Inhale, pull back, eat the smaller ranged attack instead, come back in. The fight is teaching you to treat position as a resource, and it telegraphs loudly enough that a first-time player can learn it inside one attempt.

Unintended: Wakka’s attacks reach at any distance, so a party built around him can sit at range for most of the fight and never engage the mechanic the encounter was built to teach. And the Slow counter is a line meant to punish a debuff that instead advertises it — a boss that reacts to Slow is a boss telling you Slow is worth casting.

Neither of those is a bug. They’re both paths the tree permits and the designer didn’t price. That’s what an exploit is: not a broken rule, an unpriced one.

Write the tree#

Take one boss and write its script as a decision tree — state variables at the top, telegraphs marked, thresholds as branches. Watch the fight at least twice; one pass gets you the attacks and the second gets you the order.

Mark two paths through your tree. The intended solution is the one the telegraphs point at. The unintended one is the path that wins without ever reading a telegraph. Every boss has one; if you can’t find it, you haven’t watched long enough.