What does the OGL mean for things based on d20 elements, but which aren't games?

Question

I've been thinking lately about how the Overlord novels/manga/anime are so clearly based on 3e/3.5e/d20/whatever, yet were still commercially published--and, as far as I'm aware, suffered no legal action from Wizards of the Coast. Much of the "mechanics" of the series (at least from what I've seen) are entirely possible within the parts of d20 that are covered by OGL.

An example: at Overlord's spell magic arrow

This appears to be a clear copy of d20's magic missile. It's a 1st-tier spell, equivalent to a 1st-level spell, and it launches an unavoidable bolt of non-elemental (equivalent to force damage, or not having an energy type) magic that deals a small amount of damage and cannot be blocked by normal means. The spell can also create multiple bolts if cast at a higher tier/level, just like how magic missile would (depending on what exactly the Overlord wiki means by this, possibly similar to the Spell Points variant rule, also open content)

By my reading of the OGL 1.(e), "Product Identity" (which, as per section 7, must be agreed to not have any of the following done with it, from 1.(f): "Distribute, copy, edit, format, modify, translate and otherwise create Derivative Material of Open Game Content"; 1.(b) defines Derivative Material as "copyrighted material including derivative works and translations (including into other computer languages), potation, modification, correction, addition, extension, upgrade, improvement, compilation, abridgment or other form in which an existing work may be recast, transformed or adapted") includes both the "spell" magic missile and the "magical...effect" produced by magic missile, as well as any modification or adaption thereof.

Mechanical similarity looks like it's derivative

The effects of magic arrow are clearly derivative of magic missile. But the specifics, such as dealing 1d4+1 damage (or what 1d4+1 damage even translates to, beyond rarely being enough to kill a target with one shot), or having a range of 100 ft. + 10 ft. per caster level, or any of those details which pertain to actual d20 mechanics, do not seem to be mentioned in Overlord.

This brings me back to the question, which is more general than just that single spell.
How is it that Overlord's use of things which seem like they ought to be forbidden due to being considered WotC's "Product Identity", is actually okay?

1. Is it because Overlord isn't a game (in which case, where are exceptions like this stated in the OGL?
2. Does it have to do with the fact that the above details are generalized into a written/drawn form?)?
3. Is it because magic missile isn't explicitly designated as Product Identity beyond the proper name of itself as a spell (in which case, what about spells like sleep and animate dead, which Overlord keeps the names of, or elements such as "troll" creatures with high strength and what amount to d20's Scent/Regeneration abilities?)?
4. Or is it something else entirely?

Answer 1

Here's the thing about the OGL. You don't actually need to use it just to reuse unpatented game mechanics.

What the OGL does is provide what's known in legal terms as a safe harbor, in return for accepting restrictions on your reuse of mechanics. That means that as long as you follow the terms of the OGL, they agree not to throw lawyers at you (and typically, if you violate the terms, you get a warning and a chance to fix things as opposed to a Cease and Desist)

However, game mechanics themselves are not normally copyrightable. and this has been confirmed by a court in Texas. A couple of notes here - first, I'm focusing on US copyright law because it tends to be the most prevalent in these cases. Secondly, this does not prevent you attempting to patent game mechanics, but they would likely need to be sufficiently unique for a patent to be granted (something that WotC certainly couldn't claim at the time for D&D mechanics, due to many other RPGs using similar mechanics. Granting of a patent would need a game to do something particularly innovative and unique, such as linking a random chart to a deck of cards and some physical device that scrolls through a roll of paper in order to blah blah blah... WotC have got a patent on turning a card sideways as a way of indicating resource usage in a game, for example, so that could feasibly be challenged in court.)

It's worth noting here that in addition to patents, you can still Trademark certain terms in a game, too. For example, WotC have Trademarked on the term "Dungeon Master" (which is why other RPGs use an alternative such as "Game Master".) Also, if you're not using the OGL, you cannot simply copy the text of game mechanics verbatim, as that is protected under copyright - you have to rewrite it in your own words.

So, as long as Overlord isn't actually using the OGL (and if there isn't a copy of the OGL included with the product, they're not), it's free to do anything it wants with game mechanics, and can ignore the other terms of the OGL completely. It just has to deal with the possibility that they may find a letter on their doorstep from WotC's lawyers due to a lack of safe harbor. "Product Identity" doesn't exist outside of the OGL, so they don't have to worry about using the words "Magic Missile" (note that if WotC *trademarked" that term, then they would have some legal ground to challenge it on.). There doesn't seem to be anything WotC can legally challenge them on, therefore, because they're only copying game mechanics which we've already seen can't be protected under Copyright law.

Finally, you're misinterpreting Magic Missile's status as a Product Identity term. Magic Missile (including the name) is declared as Open Game Content, not Product Identity in the 3.0 SRD (amongst others), which declares its entire contents as OGC. This means that even the names in that document are declared specifically as OGC, and therefore excluded from the PI terms - think of the PI statement as a catch-all for proper names, etc. not declared OGC in order to clarify that you can't use them. (Now, There are actually some schools of thought that believe the PI declaration overrides the OGC declaration, but unless someone challenges that in court we can't really know for sure, however the number of products using those names under OGC terms makes it pretty obvious that WotC believe it's a legitimate usage of them.)

Therefore you can create derivative works based on Magic Missile, under the terms of the OGL. That's the whole purpose of the OGL, to grant a license to make derivative works, but only for specific pieces of intellectual property rather than an entire text.

So, in the case of Overlord, they're not using the OGL, so they're not bound by the terms of it. Note that this is not because it's a computer game - they simply realized they didn't need the OGL. They could still have opted to use if if they wanted to make use of any IP that the OGL grants that they couldn't otherwise use.