Got a Rod of Lordly Might in a loot drop from a Red Dragon last night. When the first button is pressed (DMG p196) the rod becomes a flame tongue as a fiery blade sprouts from the end opposite the rod's flanged head.
But under Flame Tongue (DMG p170) it is a modifier for "any sword" and doesn't have a specific base sword. There is a Flame Blade spell (PHB p242) that acts like a scimitar but I don't think the RoLM is referencing that spell instead of the magic item.
So, what size sword does the RoLM make? A base long sword sized blade? Any sized sword? My character is a barbarian with the Great Weapon Master feat so having the RoLM become a greatsword and thus be "heavy" and enable the feat would be a big plus (as well as doing more damage). My DM has ruled that it can become any length I want but I was curious if there was official answer somewhere, or perhaps a reference in previous editions.
As a related question, can a RoLM count as a "heavy" weapon at all? None of the other weapons it can be; a mace, battleaxe, or spear are "heavy", so even if it made a greatsword sized Flame Tongue blade would it still count as a heavy weapon? Conversely, if I made it a scimitar sized blade could I then wield it as a finesse weapon?
Best Answer
While the default answer would be "work with your DM" you are already doing that.
There is no reason NOT to allow it to become a 2H version of a flame blade, since button 4 and button 5 do the following:
Button 4:
Button 5:
Between the two, they are bigger and pack a harder punch than a great sword. It is easy to argue that a 50' pole has to be at least as heavy as a great sword. (That's longer than a lot of flag poles). Your idea to interpret "any sword" for flame tongue into a great sword looks to be well within limitations and scope of that magic weapon.
The 2018 DMG errata supports this answer, in that for the Rod of Lordly Might, p. 196, DMG ...
If you chooose two handed sword, then that is what it becomes.