Pokemaster (site admin) would be able to answer this best, but he's not very active. So in the mean time, I'll post this. Formally, Pokemaster has made a stance on this on the FAQ page:
Can I use some content from your site?
In general, no. All written content, site design and data display/layouts have had a huge amount of research and effort put into them to make as easy to read as possible. Do not steal our content!
However, official Pokémon artwork and sprites are not our creations and are used under a Fair Use Policy, so you are free to use them however you like. Each of the Pokémon sprites pages has an easy way to add images to your site or forum post.
Assuming you want to use content on this website for your own original content? As above, it depends on what content you want to use. If you're looking for the site's original assets, e.g. its layout and original written content, then you cannot use the content without express permission from Pokemaster. In legal terms, this would be copyright infringement, unless it was for the purpose of commentary or reporting i.e. fair use.
However, nobody 'owns' the raw facts and statistics about Pokemon, so if you wanted to use this site as a resource for information on say, Pokemon's base stats, then you would be fine. Similarly, any artwork that belongs to Nintendo/TPCI is obviously not this site's property and should be fine to use.
There used to be a web app for this site that could be accessed offline, but that was discontinued years ago. If you wanted to use this site offline, you'd have to manually download it. If you just need Pokemon info for your work, use something like PokeAPI.
