One fact to always remember when using Balthazar to attack someone is that, though Balthazar flies, it can still be attacked by all defensive towers and monsters. Railguns and towers that deal heavy damage are very effective against them, so try to either destroy or distract the defensive towers first if aiming for bunkered monsters. Balthazar can be quite effective at destroying buildings if deployed correctly. Its 3200 health allows it to suffer much damage before it dies, while its decent 600 damage can be quite useful when taking down buildings. It is also highly reccomended to team them up with a level 6 Fomor, preferredly backed up with some Zafreeti. However, Balthazar's main usage is to be used against monsters in the enemy base's compound or to be placed into your own to defend, as they do more damage to monsters. However, remember that if there is a large number of monsters in your enemy's compound, Balthazar can be easily killed when used alone or in small groups. Bunker them for high attack power. Plus, they take only 40 spaces, so you can put 16 in a level 4 bunker.
Note: When sending Balthazars in against Drull, it is even more effective if you send something else in a few seconds before, to distract Drull (10-25 Pokeys should be enough). If it is a Gorgo, 2-4 Zafreetis are a must, considering Balthazars low health and Gorgo's massive health. If possible, use a Pokey or Spurtz Bomb to distract Gorgo. Balthazar can also be used to easily kill Fomor, regardless of the level. Lure out the Fomor with a monster so he is out of tower ranage then unleash Balthazars on it ( Around 5 will easily kill a level 5/6 Fomor), Fomor should be dead in seconds.