Here is the full list of all 12 Wonder Boy in Monster World trophies - there are 9 bronze, 2 silver and 1 gold.
Collect all the heart containers.
Finish the game.
Guard against 10 attacks by spinning a spear-type weapon.
Collect all legendary equipment.
Use all types of magic.
Find the precious Charm Stone.
Find the "Welcome to Monster World" sign.
Meet the Elder Dragon.
Meet the Sphinx.
Meet Poseidon.
Try staying at an inn without enough gold.
Do not skip the SEGA logo sequence.