The biggest hurdle for many players is finding an version of the game. Since these are Flash or HTML5-based games, they are often filtered by school or office networks. To access the game reliably:

Tell me which character you plan to main, and I can give you a specific move-set guide for them!

Great for "zoning" opponents. Use his ice-make magic to keep pirates at a distance. The Pirates (One Piece)

Some users utilize light VPN extensions to bypass simple URL filters.

Look for reputable gaming portals that host HTML5 versions of the game. These are less likely to be flagged than original Flash domains.