There are 12 Trophies that can be collected.

Bronze

Wizard    
Use all types of magic.    

Hello Poseidon!    
Meet Poseidon.    

Hello Dragon!    
Meet the Elder Dragon.    

Hello Sphinx!    
Meet the Sphinx.    

Welcome to Monster World!    
Find the "Welcome to Monster World" sign.    

A Rare Find    
Find the precious Charm Stone.    

The Great Blue Awaits    
Do not skip the SEGA logo sequence.    

Renowned Spearman    
Guard against 10 attacks by spinning a spear-type weapon.    

Have Mercy!    
Try staying at an inn without enough gold.

Silver

The Legendary Wonder Boy    
Collect all legendary equipment.    

With All One's Heart    
Collect all the heart containers.

Gold

Congratulations!    
Finish the game.

http://www.ps3trophies.org/game/wonder-boy-in-monster-world/trophies/