From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokémon Crater, often subtitled as the Battle Arena, is an unofficial online Pokémon game that is played with just a mouse. Registered players can click on maps to gain Pokémon and battle with a computer-controlled player to raise their Pokémon's levels. The site was created by webmaster Aaron in 1999. Since then, it has undergone a number if changes and is now at Version 7. Today, players can walk around a map and battle the members around them, though the actual opponent may still be controlled by the computer. Before version 4.0, only one Pokémon would be used by each trainer in all battles. However, now the aim is to beat a team of up to six Pokémon, though switches are not allowed until either one faints.
Additional features include battling Gym Leaders to collect badges and battling anime characters. Healing items can be bought, along with Pokéballs. Master Balls are available, though they are actually closer to the Ultra Balls of the game in effectiveness. Each member of any species of Pokémon will always have the same four moves, which can be checked using the site Pokédex. The main aim is to get onto the Top Trainer's list and/or complete the Pokédex, though that is a very hard feat to manage. It is even harder than in the games, because your Pokédex counts only the Pokémon you have, not the one you have evolved or traded. Also, all 28 Unown forms are separate Pokémon, the three cloaks for Burmy and Wormadam are counted as separate, the Unique Pokémon (see below), and there are 5 forms of each species: Normal, Shiny, Dark, Metallic, and Ghostly.
In some version of the game you could now change the attack of a Pokémon via the My Account Page. This allows you to change a Pokémon's attacks with new ones. With the right amount of money your Pokémon could now have a different attack but, the price varies from Pokémon to Pokémon
The site has its own unique Pokémon, a Dragon/Ice Pokémon called Dratinice. Dratinice evolves at level 100 - a
level easier to reach than in the games - into the Dragon/Fire Pokémon Dratinire and an Electric/Dragon Pokémon called Dratilic. Until Shiny Pokémon were added, Shiny Scyther was a novelty, as this was Aaron's favorite Pokémon. Both Dratinice and Shiny Scyther could be found in a house on the maps at a specific time of the day. In Version 4.0, the houses are no longer there. This means that Dratinice can only be found in the wild, though it is rare. Shiny Scyther is found in the same as any other Shiny Pokémon, and so is just as rare. There are also four special classes Pokémon, Dark Pokémon, Metallic Pokémon, Ghostly Pokémon and Shiny Pokémon.
The site has numerous ways of battling. If you enter a house you may battle other anime characters like Tracey and Ash. Although you will not encounter any Wild Pokémon, you can still fight other trainers. If you beat a Pokémon (Wild) the Pokémon(s) used in battle will receive experience points and some money depending on the battle. Beating gym leaders (see below) will award you with a badge and twice the money you'll normally receive. The same thing with other trainers you can gain exp. points and some money. You can find Wild Pokémon by pressing the direction arrows outside of buildings.
There are two ways of battling another member. You can battle them computer controlled, in which the member's Pokémon are controlled by the computer, or live battle them, in which that member controlls his/her Pokémon. There are two ways to engage in a live batle. You can look around the map for one or you can type their username into the "Batlle an Online Member (Live Battle)" page.
This section is yet to come.
Alongside the game, at one time the site had a fairly busy message board. These were to talk and get help about the game, as well as talking about Pokémon and more general topics. The moderators, who usually worked with little interaction with Aaron, had a hard policy against spam, and were prepared to ban those who did not follow the list of rules. These boards were removed during a big upgrade in August 2004. In the anti-spam climate of the original boards, those who did post properly were noticed, and many were recruited to a private club, named Valthors by its creator, Vandurer. Three of the four forum moderators, including the most prominent, were among the members. However, with the major source of recruitment closed down, the activity level of club dropped significantly and it remained largely inactive until being officially dissolved in June 2007. A new message board was set up in March 2006 but this did not have Valthor influence.