  Board games are a great source of entertainment for all ages, as they create
a competitive and engaging environment, as well as stimulating learning and
strategic thinking. It is common for digital versions of board games, as any
other type of digital games, to offer the option to select the difficulty of
the game. This is usually done by customizing the search parameters of the AI
algorithm. However, this approach cannot be extended to General Game Playing
agents, as different games might require different parametrization for each
difficulty level. In this paper, we present a general approach to implement an
artificial intelligence opponent with difficulty levels for zero-sum games,
together with a propose of a Minimax-MCTS hybrid algorithm, which combines the
minimax search process with GGP aspects of MCTS. This approach was tested in
our mobile application LoBoGames, an extensible board games platform, that is
intended to have an broad catalog of games, with an emphasis on accessibility:
the platform is friendly to visually-impaired users, and is compatible with
more than 92\% of Android devices. The tests in this work indicate that both
the hybrid Minimax-MCTS and the new difficulty adjustment system are promising
GGP approaches that could be expanded in future work.
