The following are known glitches in II.
NES version glitches
No Random Encounters
In a new game, if the main character is named 'TUT' and the speed of the messages is set to 'fast', the game's RNG variable will not be functional until the game is saved. This allows all the random encounters to disappear. Another harmless effect is that all movable NPCs will only move down in each screen.
Duplicate Water Flying Cloth
In a single play through, you can obtain a second Water Flying Cloth. To do so, right after giving the first set of materials to Don Mohame, go back to the 3rd floor of the Dragon Horn Tower to get a second Dew Yarn before saving. Now you can save, reset the game, get the first Water Flying Cloth and get go second Magic Loom. You then take the second set of materials to Don Mohame to make the second cloth after saving and reseting.