Hello I'd like to get some advice because we're developing a game called "Dungeon Boss Fight" and we recently discovered that a game named "Dungeon Boss" is already available in mobile by Bigfish Games, the same place we are going to release our game. I've used this website (http://tmsearch.uspto.gov) and found that there isn't a trademark for "Dungeon Boss". Now is it safe to release our game with the current title or should we change it? Or should we trademark our title "Dungeon Boss Fight" and hope for the best? The other game came out 5 years ago btw.
Trademark law doesn't offer a yes/no answer in this case.
Can they sue? Yes. Can they win? Yes.
Will they sue? Only one way to find out. Will they win? Only one way to find out.
Will it cost you money if they sue? Yes. Will it cost them money if they sue? Yes.
Here's a case of how far some companies go to "protect" their trademarks.
In my personal opinion, Dungeon Boss Fight is not a great name anyway, so just find a better name.