What is the ruling for Warhammer base size when GW has not produced an official model?

Question

I understand this ruling, which is pretty normal for Tournaments:

•Models must be played on the bases provided with them.

In my specific case, there are quite a number of Tyranid Special Characters that have never had a model created for them. For some of these monsters, it seems fairly straightforward: The Doom of Malantai would have a Zoanthrope Base, the Tyranid Prime would have a Warrior Base.

There are also some existing models that used to be released with smalled bases: The old Hive Tyrants (Square base, and warrior size base) would up-size to the the current Hive Tyrant large base.

For models like the Harpy, Parasite of Mortrex; I'm not sure about. The flavour for the harpy says it's a lighter Monstrous creature, that is related to the Trygon. Would it use a Trygon base? or a Hive Tyrant base? Is the Parasite of Mortrex a Gargoyle base? or a Warrior sized base?

I've never seen any official ruling on this. Since these models are all custom conversions, it seems somewhat open to interpretation.

What size base should I be using for models where the base size is not clearly defined?

Answer 1

There's no hard and fast rule for it. I would suggest using a base size most appropriate for the size of the model. So if the model is Terminator sized, use a 40mm, if Dreadnought sized, use a 60mm. So convert your model and use what makes sense.

This requires a bit of good judgement and common sense. If you made a reasonable selection most people will be OK with it in a friendly game. Though you should always check with your opponent before using something non-standard. If you plan on using your converted models in a tournament, contact the tournament organizer before hand to get a ruling.

As for units that used to be released with different base sizes, you are still free to use the base they came with, but I would recommend re-basing with the most up-to-date sizes. This will keep things consistent if you ever need to mix and match new and old models.