Started working on a small boss guide, but I'm not sure if I'll finish it. We'll see. I've only done the first 5 bosses so far.
Ultima Shadow's FFIV DS Boss Guide
Mist Dragon:
No real strategy needed. Bring a few potions, then just wack away with normal physical attacks with both Cecil and Kain. Once the Mist Dragon ”turns into mist” (the dragon becomes a white cloud), stop attacking and just wait until it turns normal again. If Cecil or Kain's HP get too low, just use a potion. Seriously, as long as you don't attack during the mist form, this battle should be piece of cake.
General and Soldiers:
You're up against a General, who does nothing but give orders, and 3 soldiers who attack at the General's command. This battle is actually even easier than the previous one. Just attack two of the soldiers until they go down, then kill the General, and finally the last out of the 3 soldiers. If you don't care about the extra EXP and having the General added to your bestiary, you can just kill off the 3 soldiers, and the General will escape. If you take down the General first, the soldiers will get confused... but I still recommend taking down 2 of the soldiers first to reduce the damage you take since the General has a lot more HP. Still, this battle is so easy that you can win by just spam-pressing the attack button. Whenever you decide to kill the General or not, you shouldn't have any trouble.
Octomammoth:
Make sure your party is fully healed before this battle. Unlike to the two earlier boss battles, this one could actually require some preperations. Make sure you got the Hades equipment for Cecil (found in treasure chests in the cave you've been passing trough). Also make sure that Cecil is in the front-row while both Rydia and Tellah should be in the back-row. The weakness of this boss is obviously the ”thunder” element, so have Tellah either spam his Thunder magic, or have him use ”Recall” and hope for a powerful high-level spell. Only use Tellah for healing if you find yourself in a tight situation. Cecil should activate his ”Darkness” for more powerfull attacks, and then attack physically. Use Rydia for healing when needed, and use her Thunder spell if you feel like you can do without healing for a turn or two. But be sure to keep your party at high HP after Tellah's in-battle dialouge, as the Octamammoth's attacks will get a bit more powerful after that part.
Antlion:
If you attack this boss head-on, you'll soon notice that it will counter your moves with a very powerful attack. The key to avoiding this, is watching its eyes. When the Antlion's eyes are red, it will counter magic attacks. So just have Cecil attack physically and Rydia defend or cast Cure. When the eyes are white, it will counter physical attacks. So just have Rydia cast Blizzard and Cecil defend or use his ”Darkness” move. The spoony bard should just use his ”Life Anthem” song over and over to help keeping the party's HP up.
Mom Bomb:
Up to this point, you might have wondered why some people consider this game too hard. Well, the battle ahead is one of the reasons. This is one of the tougher bosses in this game and by far the hardest battle up to this point. All the earlier boss battles are just pushovers when compared, so make sure you're prepared. At first, it will seem like you're just up against a regular ”Bomb” enemy. However, after a few attacks the bomb will transform into a large, cloud-like creature, and a countdown will start. When the countdown finishes, the Mom Bomb will explode, dealing massive damage to your entire party. This is the part that makes this battle hard, since if you're not prepared, the explosion will most likely end with a ”Game Over”. Some people think that you have to finish off the Mom Bomb before it explodes, and that's why they keep failing. The explosion can't be avoided and thus you should only focus on surviving it. After the transformation, heal up your entire party and have everyone use ”Defend” except Yang who should use ”Brace” instead. Hopefully, this will keep your party from getting wiped out by the Mom Bomb's explosion. After the explosion, the Mom Bomb turns into 6 regular Bombs, 3 red ones and 3 blue ones. These are no more powerful than the bombs fought in random battles earlier, so just use blizzard and Yang's kick etc until they all go down.