A little over a century ago, the Mythlanders thought to mine deeper into the East Core Quarry than they ever had before. As they reached deeper, they found a particular type of tree that burrowed its way through the rocks...never piercing the surface above. In these trees were veins of pure Indicore, a substance of unconfined power. In fact, its amber is thought to be the origin of Seeker Stones and the spark of power in energy of all types. Even more startling, they found a race of cave dwellers that had never seen sunlight. The Mythlanders, in their greedy ways, corrupted the East Core Abyss and all its inhabitants. Not even they were prepared for the fearsome Abyss Troll that lived below. What an ideal hiding spot for the shards that could defeat the Master Shadow.
Basic Energy and Static Volt can only attract Glitch Goblins in this location. To attract other characters, seekers must use appropriate E.C. Abyss energies. The only energy available for purchase is E.C. Abyss - Tier 1, while others are available as loot from characters in the previous tier (see table above) - e.g. E.C. Abyss - Tier 3 can be looted from characters in the 2nd tier (Chipstone). There's a total of 8 tiers in the Abyss.
In every tier (except the 8th), there's a rare (less common) character. They are actually Rare Characters from other locations, but in here they drop a larger amount of tier energy and they also have a 100% chance of dropping the tier-related shard (unlike other characters). They are not to be confused with characters considered rare in other locations like Trog Scavenger or Groganon. These do not qualify as tier rares since they don't drop anything special. Note that East Core Abyss will still have a unique rare character once Chapter 17 is released.
Creatures of the Mudrock tier are quite weak and can be easily defeated. The strongest character is Toxic Phun Gai (63 attack). Sulphur Construct is the rare character in this tier. It's best to focus on equipment with high defense power (traits) to achieve a 100% win rate. Blessed Chakra, Pandora's Jar or Singing Clarent are great options, but other weapons (premium or not) will also suffice.
Chipstone tier is slightly more challenging, mostly because Magma Runner appears here. Because of that, using Solstice Sword is the best option, but non-premium weapons like Pandora's Jar can also be used. Burrowing Beetle is the rare character in this tier.
Flatrock tier is a little easier than the previous tier, since the strongest character of the tier is Iron Ant (59 attack). Generally, it's best to use equipment that will boost your defense power to achieve a 100% win rate. The best weapon to use here is Blessed Chakra, but other weapons like Singing Clarent or Pandora's Jar can also be used with success (especially because of their defense traits). Dark Dig Dwarf is the rare character in this tier.
Characters in the Deepstone tier are stronger and weak to either Strong (Fathom Pixie and Legion) or Precise weapons (Monstrous Fossil). The best way to deal with this is to use a Strong weapon and get your defense power to 77 or more (which is enough to beat the Monstrous Fossil). This is very hard to do without any premium items, but it can be easily achieved by simply using the Solstice Sword. Dust Moth is the rare character in this tier.
Chrushrock tier is very challenging. Glow Worm is weak to Precise weapons and Shubb'Ngohlth is immune to all weapons with a power type except Ice. Therefore, the best regular weapon to use here is the Catapult, while the best premium option is the Assassin's Crossbow (Excalibur or Pitfall are also decent choices). Amber Sprike is the rare character in this tier.
Using a Strong weapon to defeat the characters on this tier is highly recommended. Again, Solstice Sword will work great because of the Shadow Parasite. The best regular weapon to use here is the Singing Clarent. Feldspar Worm is the rare character in this tier.
There are only two characters on this tier, and none of them have specific weaknesses - any weapon classes/power types can be used. However, since Corrupted Miner is a Dark enemy, using an anti-dark weapon like Solstice Sword (premium) or Pandora's Jar (regular) is recommended. Feldspar Ogre is the rare character in this tier.
The only enemy on this tier is the Abyss Troll. He is very powerful and doesn't have any weaknesses. The best weapon to use against him is Blessed Chakra - since it's currently the best weapon to use when facing Beast characters. Also, it's best to use Harvest Ring (limited edition) as support and a powerful potion like Galactic Goo, Spring Showers (premium) or even Dragon Acid. Note that the drop rate of Black Ravoth Shard is 50%, so defeating the Abyss Troll more than once might be necessary to complete Chapter 16.