The large bomb enemies that appear in Chapter 3 are bastards. Had to redo this fight once because the thing insta-killed Wal when it detonated. I could swear he was at full health too! But I suppose the problem is the Thief has no defense. ^^;
Mobius Final Fantasy – Big Bomb
koukoupuffs 
hello, how do you pass this Big Bomb ?? i’m stuck in chapter 3.2 because of big bombo x 3 in a battle
There are many options that can help. Any of these or a combination of some can work~!
– use a job with an Ultimate Attack that hits all enemies. You can fight in another area to max out the Ultimate Attack gauge before fighting the 3 bombs. It’s best to use this after the Break Gauge is in its deep red colour. Use the attack to knock them into the Break Phase and then use element cards that the bombs are weak against to quickly defeat them.
– use high defense Warrior job such as a Knight or Paladin
– use jobs and cards with high Break Power to take out the Break gauge quickly. When any of them are about to blow up, putting them into Break will “reset” them.
– use any cards that can slow or stun enemies such as Yasha or Nekomata (http://altema.jp/ffmobius/slowandstan-4184)
– use support cards like Barrier (バリア), Wall (ウォール), or cards that even have both of them like Hellgate (http://altema.jp/ffmobius/ability/982) to reduce the damage taken when they explode.
Cards with Barrier: http://altema.jp/ffmobius/abilitydata/44
Cards with Wall: http://altema.jp/ffmobius/abilitydata/109
The table at the top of each web page has links to the cards’ individual pages.
– You may even want to use debuffs like Debarrier (http://altema.jp/ffmobius/abilitydata/64) or No Guard (http://altema.jp/ffmobius/abilitydata/215) or DeBrave (http://altema.jp/ffmobius/ability/556) to weaken their defense or attack.
Oh, it’s probably best to deal with each bomb individually if you’re not strong enough to kill them all off in one hit because lowering their HP will increase the chances of them setting themselves off.
Good luck! ^_^