You fight this beast inside the Enchanted Swamp. This boss' pattern is very easy to learn but timing your charged attacks and aiming right will be your biggest challenge.
-Gigaflea moves horizontally in your direction and stops to spit 5 gooey projectiles in a straight line. Keep moving left or right to avoid getting hit.
-Every now and then a blue fly monster will appear and chase you. You might want to defeat it fast with a carefully timed charged attack.
-My personal strategy is to face Gigaflea and send a Lv1 charged attack upwards when the beast is about to start moving. Time your attack carefully to damage him and quickly move one step to the side to avoid his next spits. Repeat this simple strategy until the boss is dead.