RTF is a global modification that replaces all towns in the game.

you need to add files in the scripts and MapObjects folders (so that the unit appears in the map editor)

rework the files in the GameMechanics, Cameras folders, paths inside the folders also need to be renamed where required (so that the unit actually works and the camera is correct)

and specifically in the folders with units (these are new_creatures) there are creature.(AdvMapMonsterShared) files, in them you need to enter the number in the line <Creature>CREATURE_XXXXXXX</Creature> (otherwise an elven unit will be placed on the map instead of NCF)

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there are also nuances with stats, that is, you need to set a neutral town, write out upgrades (currently vanilla units are written there, you need to substitute NCF creature numbers)
you can compare 2 mods - this is the toad and the NCF toad