Monster template — A saved recipe that turns a standard creature into a reusable variant.

You start from an official base creature, then define what’s different—gear, abilities, tweaks to their stat block, flavor text, and so on.

When you use that template on a creature in play, those differences replace the matching parts of the base stat block, so you get a consistent “same guard, different loadout” or “upgraded version of this beast” without rebuilding every stat block from scratch.