In the final showdown in The Good, The Bad and The Ugly, we learn after the shoot out scene that Tuco's gun was empty. But Tuco didn't know that. Who was he trying to shoot at?
In this question Who was Angel Eyes trying to shoot first? the TS assumes it was Angel Eyes. But if Blondie would trust Tuco to shoot at Angel Eyes, he wouldn't have needed to remove Tuco's bullets from his gun. (Although Blondie uses the situation to his advantage later too to make Tuco do the digging and protect himself from potential dirty tricks from Tuco's part.) Also, if Tuco assumed that it were to become a "last man standing" situation, he must have realized that he was the worst shot of the trio and his most sensible choice would then be to shoot Blondie just after Blondie would have killed Angel Eyes.
I cannot tell from the movie scene who Tuco was aiming at. His body seems to be oriented towards where Angel Eyes was standing, but because he is trying to get his gun to fire, it is not entirely clear whether he was also trying to fire in that direction. Is there any evidence in or outside the movie that shows who Tuco was trying to shoot?