I have been trying to remember this TV show I watched as a kid, maybe around year 1998-2000.
It's about this kid who works for this scientist/professor and they collect/battle monsters.
I can't exactly remember the details, but I can tell of an episode where they battle a sphinx who tells the kid a riddle about "what goes on four legs in the morning, two legs at noon, and three legs in the evening," which is a spinoff from Oedipus. I can also remember the kid having a hammer-like weapon.
You're thinking of Flint the Time Detective.
The series is centered around the adventures of Flint Hammerhead, the "Time Detective", a boy from the prehistoric era who was resurrected from a fossil and became a Time Detective, although his competency as a detective is dubious. Much like Inspector Gadget, much of the heavy thinking is done by Flint's friends, Sarah and Tony Goodman, who accompany him on his adventures. Flint, however, pulled his weight in battle, when he would fight with the aid of his father Rocky Hammerhead, whose partial resurrection left him a sentient, talking rock with a face. Rocky, fashioned into a hammer for Flint, served Flint as both sturdy weapon and adviser, the latter both in and out of battle. Flint's job as a Time Detective was to go back in time and convince time-shifters- cute, collectible creatures - to ally with him to protect the timeline.
In the US, Flint the Time Detective aired from March 5, 2000 until November 5, 2000. The series also aired in the Philippines via GMA 7 and dubbed in Filipino language which rans from late 2000 until mid-2001.
