Forgotten Catacombs

Forgotten Catacombs provide many of your most useful pieces of gear in rings and trinkets. You acquire these items by gathering Crypt Tokens and spending them in the crypt shop. You receive crypt tokens by defeating bosses of increasing difficulty every 5 floors. Your first set of crypt rings and trinkets are available at lvl 20, when you will feel like you can't get past the annoying lizard boss on floor 25. Don't fret, because as soon as you have gathered up your lvl 35 pvp set, he should fall easily.

Once you reach floor 50, and every 5 floors you will encounter the same annoying boss. A giant floating eyeball that has several very annoying skills that it will use against you and your troops. First thing to note on fighting this boss is that the majority of it's attacks will focus your back row. If you like to stand behind your troops to fight, this means that the full brutality of this bosses heavy magic attacks will be focused on you. For the best chances of survival, adjust your troop formation so that your troops are behind you, allowing you to unleash your fury against the boss while your expendable pets get blasted by lighting.

The bosses attack rotation is fairly set,
Round 1 Back row Lightning Bolt
Round 2 5 hit AOE attack with chance of stun
Round 3 Back row Lightning Bolt
Round 4 Random target debuff attack, which gives a -50% to Patk, Matk, Pdef, and Mdef
Round 5 Back row Lightning Bolt
Round 6 3 hit AOE Tentacle Slap (This is the only Physical attack this boss uses)

From this point on the pattern will effectively repeat itself untill you reach the last bar of the bosses health, where he seems to throw an extra debuff into the rotation.

The best way to receive the maximum rewards for your efforts in the Catacombs is by using an item called Crypt Key, which doubles the rewards you receive in the crypt. These relatively rare items should be conserved early, when you are stuck pitting yourself against the first 50 floors and the rewards you receive are minimal. Once you are making your way passed the halfway mark, the crypt key can help you maximize the gains of your efforts without feeling like you wasted 8 keys trying to get to lvl 50.