Dragon Warrior IV (NES)

Dragon Warrior IV was phenomenally popular in Japan as Dragon Quest IV, but wasn't released in the west until late in the NES' lifespan, when most non-Japanese gamers were already occupied with 16-bit platforms.

Nevertheless, IV featured an innovative (for its time) chapter-based story system and continued the series' tradition of solid gameplay, eye-catching monster designs, and a memorable soundtrack. It was later remade for the PlayStation in Japan only, but that version was later ported to the DS and released internationally.

Debug Features
A debug mode can be accessed with Game Genie code. When you start a new game, you will be given a chapter selection menu. If you press B at this menu, you will start at Chapter 5 with a full LV1 party, and the hero gets 65535 HP and MP, all spells available, and all return destinations available. If the hero is healed, he will lose the 65535 HP.

Otherwise, if you get to Chapter 5 and skipped earlier chapters, the characters from the previous chapters will join the party with 0 for all stats, including HP and Max HP, making them useless.

While using the debug code, you can also hold B to walk through walls, and the Return list is in a different order and has additional destinations.

Unused Enemies
Nine unused enemies are hidden away in the code, almost all of which were intended to be fought on the ocean aboard your party's ship.

Batoidei
A palette swap of Guzzle Ray and Raygarth.

Giant Octopod
A palette swap of Elefrover and Tentagor.

Infsnip
A palette swap of Armor Scorpion and Metal Scorpion.

Necrodon
A palette swap of Pteranodon and Chillanodon.

Rabid Roover
A palette swap of Poison Lizard and Baby Salamand.

Sealion
A palette swap of Great Ohrus and Sealthrope.

Seaworm
A palette swap of Giant Worm and Sand Master.

Troubadour
A palette swap of Roric, minus a weapon. Of the unused enemies in this game, he is the only one who was not intended to be fought on the open sea. Instead, judging from his total lack of action during battle, he was probably inserted by the programmers to test battle scripts during pre-production.

For the record, he's one of the few human opponents in the Dragon Quest/Warrior series, despite never being used in a final product.

Zapangler
A palette swap of Bangler and Piranian.