These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Besides the original game enemies, you've got worse versions of Darknuts, Wizzrobes, and Octoroks to possibly contend with.
With the enemy editor, it's possible to create your own Demonic Spider.
Good Bad Bugs: There have been several bugs that benefited the player over the course of the program's lifespan.
The biggest one comes in the third quest. Here, the warp points are still programmed in the first quest spots, and not where the levels actually are. After getting the recorder from Level 4, you can warp to where Level 4 was in the 1st quest, meaning you can get the letter without having to retrieve the raft from Level 5. This was fixed in the fourth quest, partly because it stowed away a heart container instead.
Growing the Beard: As the program aged, it added items and elements found in other Zelda games, most of which were met with positive reception. It also squashed some serious game-breaking bugs.
That One Boss: Level 6 of the Fourth Quest has you fight a Giant Moldorm with forty segments. It takes up most of the screen and the fight can take forever. If the player dies, he or she will have to fight the boss again with the segments restored.
That One Level: Levels 2 and 8 in the Third Quest. Level 2 has the player fighting Wizzrobes early, while Level 8 has fireball shooting statues in nearly every room in the level, thus disrupting the player at every turn. In the Fourth Quest, there is Level 6, which not only has the Giant Moldorm boss battle listed above, but it also houses souped up versions of the notoriously weak Stalfos/Goriya/Rope enemy set. To put it in perspective, blue Wizzrobes take three hits with the magic sword to defeat; Rope 3s take five hits, and they have not lost their speed, either.