I would not go so far as to say that Decayed Dungeon Gaiden/Side Story is actually a Zelda clone. It seems to be a dungeons-only Zelda relative. And it seems like an old-school, multi-tier dungeon like in Bard's Tale or Wizardry type of construction.

There are boss fights along the way, and they look impressive in terms of size, if not color.

this is another Habit Soft game, which have really nice quality cases and labels for a modern production company.