Type 2 links or sub-universe links are a type of link that happen when elements from a series appear in another series, but only as fictional things within its universe. This is the second strongest and most relevant main type of link (therefore not counting Type 1.5 links) between series, since even if elements appearing are not "real", as opposite to Type 3 links, they are the actual elements from the other series, and not imitations. They are only directional since they always involve elements appearing from one series to the other.
Sub-universe links happen when an element from a series appear as being fictional within another series. An example is when characters in a movie are seen playing a specific videogame, reading a comic or watching a movie, indicating that in that movie's universe those series are fictional.
For a reference to be considered an actual type 2 link, the referenced element has to be the actual original one, and not an imitation (or else this would be a Type 2.5 link), unlike Type 1 links, however, type 2 link don't strictly need the authorization of the copyright holder of the referenced series to be considered actual. This happens because many times fictional works reference the actual series, for example by showing actual gameplay footage of a game, or the actual cover of a book, even without authorization, and in these cases we can't say it's something based on the other series but not actually it, since it clearly is actually it.
As already said, a sub-universe link happens when something from a series is proved to be fictional within another series, but it also happens when a series cites an element from another series and it can't be proved to be real. For example if a character in a Series X tells to a mustached man "You look like Super Mario!" this means that the character knows who Super Mario is, but it doesn't prove that Mario is real within Series X, since he might simply be saying that the man looks like the video game character, Mario. So even if we don't have prove that Mario games exist within the Series X universe, we can't prove that Mario is real within that universe and therefore, in doubt, we consider the less strong link.
Type 2 spin-off
Sub-universe spin-offs happen when a series uses elements from another series as defining for itself, while still considering them fictional. It shouldn't be confused with the opposite Type 1.5 spin-off, that's about a series based on fictional elements from another series.
An examples of Type 2 spin-off may be a work about the author of a certain work. Notice however that it has to be a fictional story, not a biographical one, or else it's ignored in this wiki. Another example may be a movie about a great fan of Spider-Man comics, that wants to be a superhero too. Notice however that for this to be considered a spin-off and not just a regular reference, the series must be written around the other one and use it as a base: if the story is about a fan of superhero comics in general, with Spider-Man being just one of them, or just being chosen at random by the authors, this is just a regular sub-universe reference.
This type of link is often ignored by people, especially in realistic works, because, being based on the real world, the presence of a fictional work within them is not more notable than the presence of any other real world element, such as cars and houses. This is wrong, though, as due to licensing issues, it often happens that a fictional work, even if totally realistic, features original works that don't exist in real life, basically meaning that the overall work of fiction within that universe is totally different than it is in real life. The mere presence of an actor in a movie may imply that within that movie's universe that actor doesn't exist, so all his previous works are either unexistent or star other actors. This is pointed out in Last Action Hero, where the main character Danny finds himself inside a movie starring Arnold Schwarzenegger, and in a scene he's surprised to find out that within that universe, the movie Terminator 2 is played by Sylvester Stallone instead (see Last Action Hero X Terminator).
Analyzing the canonicity of a type 2 link means indicating the consequences of a certain fictional work existing within the other series, and how it would likely be changed to exist in that universe. This however mostly applies only to series that also have another type of link between them. For example if a character from a Series A is seen reading a comic book of Series B, and then a direct crossover between the two happens, then it should be noted how elements from Series B can be both real and ficnional for Series A. This usually means that either the crossover happens in a totally different continuity, or that the only scene of the comic is removed from the official continuity. Notice that it does get useless however to go into too deep detail especially if the work features fourth-wall breaking, sometimes making these references "just a joke".
Also notice that if a reference is considerd sub-universe link only because of lack of evidences for an in-universe link, it doesn't exclude the possibility of elemnts from the two series actually existing together.