Behaviour

A def may carry rules: things that happen to it — it turns into another of the mod's defs, spawns units, heals, pays, takes a buff, blows up — when something happens to it (on), when a condition comes true (when), on a clock (every), or when the player presses a button on its card (button). The words are a closed vocabulary checked when the mod loads, so a rule can only do what the game already does safely; there is no scripting, a spawn never takes a side past its population cap, and the game's own units have no rules at all.

Changing form

A tank that is a tree while it stands, and a tank again when it moves or fires — two defs, each turning into the other. The sheet's anims show the tank's frames while it moves and the tree's while it stands; the disguised form is untargetable, so nothing on the other side can pick it out:

{ "id": "mymod-mirage", "extends": "mbt", "name": "Mirage Tank",
  "rules": [{ "when": { "still": 1, "quiet": 0.8 }, "do": { "morph": "mymod-mirage-tree" } }] },
{ "id": "mymod-mirage-tree", "extends": "mymod-mirage", "name": "Mirage Tank", "producedBy": [],
  "untargetable": true,
  "rules": [{ "when": { "moving": true }, "do": { "morph": "mymod-mirage" } },
            { "on": "fired", "do": { "morph": "mymod-mirage" } }] }

A hero that ranks itself up from its card: each button is a tile showing the form it makes, paid as the work is done like production, and it waits for what it requires:

{ "id": "mymod-hero", "extends": "mbt", "name": "Hero Tank",
  "rules": [
    { "button": { "cost": 600, "time": 20, "ai": true }, "do": { "morph": "mymod-hero-gunner" } },
    { "button": { "cost": 900, "time": 30, "requires": ["radar"] }, "do": { "morph": "mymod-hero-sniper" } }
  ] }

A change of form (morph) keeps the unit: its selection and groups, its kills and rank, its health's share of the whole, and the orders the new form can carry out.

Spawning

The dead rising for whoever killed them is { "on": "destroyed", "do": { "spawn": { "unit": "mymod-zombie", "side": "killer" } } }; a nest that breeds is an every with a spawn; a car that arrives crewed is { "on": "created", "do": { "spawn": { "unit": "…", "count": 4, "into": "hold" } } }.

Shields

A def may have an energy shield that takes harm before the hull, and a regen that mends it.

A carrier's wing

A unit may carry a wing: planes of the mod's own that it keeps aboard, sends out at what it fights, takes back to rearm and makes again when lost — a light carrier's drones, a destroyer's one anti-submarine plane. The planes fight as units of their side, but they are never the player's to select or order.

Reference

A rule (defs[].rules[])

Exactly one trigger. A when runs the moment its condition becomes true and not again until it has been false; one held back by its if or its cooldown tries again while the condition still holds. An every counts from the unit's making or its last change of form. A rule's do runs in order and stops at a change of form.

Conditions (when, if)

Near (when.near)

What stands near the unit, measured to the other's edge: a flyer that takes off only with something to hook onto ({ "kind": "building", "within": 8 }), troops that fight harder beside their commander ({ "units": ["mymod-captain"], "side": "friend", "within": 10 }), a wall that wakes when its master comes by. An enemy is counted only when its side can see it.

Effects (do)

A spawn (do.spawn)

A button (rule.button)

A shield (shield)

A carrier's wing (wing)