An explanation of the strategy for the Archangel Tentaluchus boss fight.
Tentaluchus will spit ink bubbles at you, which you can pop with your sword, or deflect with your shield, to get more bombs. Sometimes Tentaluchus will go underground, and mounds of dirt will move around. You can throw bombs at these to make tentacles come up, which you can kill with your sword. When Tentaluchus reappears and sticks his tongue out, you can throw a bomb into his mouth. When Tentaluchus drills around the room, move to avoid him.
If Santaquiel is the boss of the fourth dungeon or later, there will be a second phase of the battle. In the second phase, when Tentaluchus becomes a flying UFO, avoid the sparks. It will eventually grab you in a tractor beam. Run away from the beam, then throw a bomb into the tractor beam.