Here we have the infamous Pikablue! Yes, back in the year 1999 when rumors on a young internet world spread about the new monsters for the upcoming pokemon games, people started to guess what the monsters would be called. We only had so many websites back in the day claiming they knew the names of the new pokemon and Marill was right there in the front of the pack especially for the peculiar name it claimed to have. Pikablue was the name! We later found out it was Marill due to either the Pokemon official names or the anime series when it debuted in season 2 during the Orange Islands saga.
Furthermore, Marill (Pikablue) is a very peculiar Pokemon which has multiple evolutionary forms. You'll find Marill in the wild quite easily but will need to breed your Azumarill or Marill while they hold the Sea Essence to obtain the baby form Azurill. Each games seem to carry it so you will not have a problem coming across it. The Pokemon is not the strongest of the water pokemon but they do carry a lot of HP under their body of fat. Speaking of body of fat, some of them carry that as an special ability so make sure you find out information about each ability in order to use them to your advantage.
The Pokemon is quite easy to level up and can do a lot of damage to your opponents fire pokemon. i don't recommend it for other pokemon unless you use ice moves on dragon types. Be sure you add a move to increase the defense or attack of that pokemon. It may help with the speed but the pokemon is slow from the beginning so you won't have much of an effect, I suggest you build up your defenses and take advantage of the high 300+ HP. So that should do it for now, I hope some of these tips help you on your quest to becoming a pokemon master.