To change your class you can either -
1. Go to the desert town and make a deal with the demon.
2. Collect the four treasures, kill the demon in the desert, and then go to the far north town which is empty and make a pact with the angel.
Use the oasis to hunt for materials to craft into items and to trade in the local tribal camps.
Beware of monsters within the oasis, they will appear at random to fight you, though you can run from them.
The better equipment will be in the dungeons, however they may not provide 'effects' and such, so sometimes the lesser equipment may be best.
If you save the bison the storyline will become extended. Won't spoil, but this is the only way to get any of the intimate scenes in game.
There are three 'shrines' that seal powerful monsters and a optional boss, beware them if you are alone.
There is a special cavern with an optional SUPERBOSS more powerful than the final battle. Take care if you find this place.
You can sleep in bed and randomly get an intimate bathing scene, its random to get it, but you will know it once you do.
Defeat the king rat in the capital.
Feed Dog in Capital a Bone gained from defeating a skeletal enemy in shrine of heroes.
Defeat Knight Commander Clover in Duel.
Feed Dog in Basil's Sanctum a Bone gained from defeating a skeletal enemy in shrine of heroes.
Give Soul to Ba'al in southern desert town.
Feed Dog in Knight Commander's Fortress a Bone gained from defeating a skeletal enemy in shrine of heroes.
Main Endings - Once you collect the three crystals from the forest, snow mountain and volcano, you can return to the town and either empower the seal, if you have allied with the empyrean who speaks to you outside of town, or simply give them to Ptolemy.
Side Main Endings - If you side with the empyrean and empower the town's seal you can choose to speak with Ptolemy and battle him.
Bad Endings - Most enemies within the continent attempt to corrupt Derrick, if said corruption reaches 100 then you will get an ending.
Special Ending - There are various special events which trigger within the Orc Fortress and southern passage cave. You know will get a trigger for them by scavenging.
Good Ending -
Obtain a sacred coin one of the various Mega Boss enemies that can be found within the 4 main dungeons by way of killing 10+ visible enemies within the dungeon and then giving said coin to the old crone within the sacred temple for a red feather.
Bad Ending -
End the game without doing the above.
Worst Ending -
Do several night sweeps throughout the city by resting in bed until you are captured three times by an unknown enemy group.
Alternate endings -
Do the above, but donate several hundred coins to the beast god's donation box, until he bequeaths you with a special elixir. Drink it A.S.A.P.
Will also allow for certain intimate scenes and additional dialogue throughout the story.
Howdy hey there.
Sorry for the late reply.
In order to pass the pirate ship, you need to save a maid in the fort area who is being assaulted. Save her, go up and find a demon in the fort. He will tell you about a special storage area. Steal the key to said storage area from the fort commander's room, go out and around the fort to the center back and the head down. Interact with what you find there and then continue with the pirate invasion as normal.