A game with 8 players.

has anyone tested how OX works when creating alliances? will there be bugs when transferring money or redeeming heroes in another Castle; I think exchanging artifacts will be impossible with OX, but bugs might occur when allies meet for retraining spells, for example.

Well, tournaments were played with alliances, and everything was fine. And generally, this is HotA, there are tons of bugs here, you won't find them all at once.