Zelda II: The Adventure of Link
Zelda II: The Adventure of Link
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Did You Know Gaming? Feat. JonTron
 
The Infamous "I am Error" quote is actually his name, the other man you can find there, "Bagu", is Japanese for bug. This was likely an inside joke, making them "Bug" and "Error".
On the game over screen, a silhouette of Ganon is displayed along with the sound of him laughing. This laugh was taken (and slightly altered) from Punch-Out!!, where it was used as Soda Popinski's laugh whenever he wins by knock out.
Contributed by Kakariko Kid
The Famicom Disk System release uses different battle music than that of the cartridge release for the NES. The reason for this change is unknown. The song was eventually remixed and used as the mini-boss theme in The Legend of Zelda: Minish Cap.
Contributed by Takahashi2212
Thus far Zelda 2 is the only official side-scrolling Zelda game. Link: The Faces of Evil, Zelda: The Wand of Gamelon and Zelda's Adventure were all also side-scroller Zelda games for the Phillip's CD-I but these games are not considered official Zelda titles by Nintendo.
Contributed by VNRob
Zelda II: The Adventure of Link is the only game in the The Legend of Zelda series, excluding spin-offs, without the word "The Legend of-" in the title. It is also the only numerical sequel (marked by the roman numeral "II") in the Zelda franchise.

However, in the Japanese release, the game does have the prefix of "The Legend of".
Contributed by pkmngmr
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Zelda II marks one of the few instances where Link has lines in a canonical game. He says "I found a mirror under the table."

In the Japanese release, this isn't the case, and it is simply a generic message stating that Link found the mirror, rather than him stating it.
Contributed by Shinitenshi
In the Japanese version of Saria Town, one of the graves in the town reads "The Hero Loto rests here." This is a reference to the Dragon Quest hero.

The first Final Fantasy game had a similar grave in the town of Elfheim. The grave reads "Here Lies Link".
Contributed by Shinitenshi
The Sages in Ocarina of Time are named after the towns in this game (in Zelda chronology however, the towns were named after the Sages).

These towns are Rauru, Ruto, Saria, Mido, Nabooru, and Darunia. However, Mido is not a sage.
Contributed by Shinitenshi
It's possible to get past locked doors without keys by using the fairy spell and flying through the keyhole.
Contributed by ecylisis
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When Zelda II was re-released on Virtual Console, the flashing colors that played during the death animation were removed and replaced with a solid red background in an effort to prevent seizures.
Contributed by Petie