I watched this a long time ago probably in 2010s either on Cartoon Network or Boomerang. It was about 3 teens having to fight other monsters, 2 guys and 1 girl.
Now I don't remember much, but the most dominant feature about this cartoon is that every time they're going to encounter a battle, the time stops and it's pretty hard to forget that feature because of course, they fought in every episode.
I hope this might find it useful but I remember one of the monsters that they fought is about a centipede look-alike and it was a robot too, it would attack by digging itself into the ground and jumping out.
Things that i remember recently:
- There was no arena of some sort where the battle took place, the place would be like a public area, let's say like a museum
- It was a stand alone monster, meaning it wasn't from any fusion
- The time stop mechanism is like an indicator of when an evil monster is near or when a battle will happen, let's say "the main characters just walking by and having a trip to a museum and then suddenly the time around them stops, meaning there is an evil monster nearby"