Extending

Most additions are new assets. Some are one small class. A few are an enum value inside the package.

No code needed

You want	Do this
A new buff, ability, item, recipe, quest, loot table, aura	Create the asset and reference it.
A new attribute (Wisdom, Luck)	Create an Attribute Definition, add a row to your Attribute Formula, grant it from items and buffs.
A new stat your items scale (bleed damage, magic find)	Create a Stat Definition. Reference it from a Damage effect’s Damage Bonus Stat or read it in your code.
A new unit tag, item tag or rarity	Create the definition asset. Tags are queried with `HasTag`; rarities sort by weight.
A new pool max or regen stat	Create the stat and bind it on your VtCoreStats copy under Resource Pool Bindings.

One class

Ability effect

[CreateAssetMenu(menuName = "MyGame/Effects/Teleport")]
public sealed class TeleportEffect : VtAbilityEffect
{
    public override void Execute(in VtAbilityContext ctx)
    {
        var move = ctx.Caster.GetComponent<VtTopDownClickToMove>();
        if (move != null) move.Teleport(ctx.TargetPoint);
    }
}

The asset appears under your menu path. Drag it into any ability’s Effects list. ctx gives you the caster, the definition, the target unit and the target point.

Damage pipeline hooks

Shields, damage conversion, procs and on-kill effects subscribe to VtUnitStats events instead of changing the pipeline. See Units and stats.

Quest objective or reward

Subclass VtQuestObjective or VtQuestReward. See Quests.

Path provider, cursor provider, combat text presenter

Each is an interface with one or two members. See Movement, Building and Combat text.

Spawner and roaming variants

Subclass VtMobSpawner or VtRoaming. See Spawning and AI roaming.

Your own random source

Loot and resource nodes accept an IVtRandom through SetRandom, for seeded or server-controlled rolls.

Enum values inside the package

These live in Runtime/Enums and are safe to extend by appending. Never reorder or renumber existing values: assets store the integers.

Enum	Then
`VtDamageType`	Add a resistance stat asset, a field on `VtCoreStats`, and a case in `VtUnitStats.ResistFor`. Without a resist stat the new type only uses the all-resistance stat.
`VtResourceKind`	Optionally add max and regen stats and bind them on VtCoreStats. Add the pool to unit definitions and spend it from your code.
`VtAttackType`, `VtArmorType`	Add multiplier cells to `VtDamageMatrix.Rows`. Cells left out are 1.0.
`VtTraitKey`	Use a high number. Set it from buff trait overrides and read it with `VtUnitTraits.GetBool`.
`VtEquipmentSlot`	Author items for the new slot. Paired slots such as rings need a matching case in `VtUnitEquipment`.
`VtDamageSource`	A label only. Set it on `VtDamageInfo` and filter on it in your procs.

Because these edits touch package files, keep the package in your project’s Packages/ folder rather than installing it read-only, and record what you changed so the next update is easy to merge.

Not extensible

VtDamageChannel (melee, ranged, magic) and VtTargetingMode (self, single target, ground point) are wired into the pipeline and are not meant to grow by appending a value. Cone and chain targeting are effects: an AoE effect on a single-target ability already gives you a cleave.

After any extension

The project compiles with no errors.
The package tests are green. See Testing.
Your own scene still plays.