Before attempting this mission, it is advisable to train up the team more than for the previous missions put together: Guy having Pyro Hail, Niven's Fling dealing about 20 damage, Darkling having Shadowport 2, Festus knowing at least Mega Shield and the Hero having more than 25 hp should help. Having the Crimson Orb and orange orb equipped could come in handy as well.
After completing mission 3, Tastidian will repeat the objective of mission 3: namely finding the Energy Golem workshop and destroying it (since last time the location of the workshop turned out to be a trap), but this time around he gives you verified information, and this leads you to the Deeper Downs. Once in the Deeper Downs, you'll be captured by the Spriggats and their leader, Cerzak, and thrown into the Bug Pit. There, you shall encounter Helena and Flint, and if you're not feeling greedy, they'll join your team.
Battle One: defeat the BugsEdit
In this battle it's easiest to kill the three Shadow Bugs before concentrating on the two Red Spriggats. It's is also noteworthy that the Bugs are resistant to Shadow attacks, whilst the Red Spriggats are resistant to Heat attacks (that is to say, they receive only 50% of the damage dealt to them). The easiest way is to use the initial Shadowling trio to attack the two Shadow Bugs on the left-hand side of the map and using the Hero to finish off at least one of them before the enemy's turn begins. Then use the rest of the team to deal as much damage to the third Shadow Bug (on the upper side of the map) as possible. Next, it's likely that the Hero could come under attack from the Red Spriggats and the remaining Shadow Bug, so Feedback may come in handy for the next several turns. Use the Shadowling trio and the Hero to deal with one of the Red Spriggats and one or the remaining Shadow Bugs on the left hand side, whilst using one of the remaining teammates to lure out the second Spriggat from the lava, so that more teammates can simultaneously attack it. In the end, use the second half of your team to overwhelm the second Red Spriggat and this should do the trick.
Battle Two: defeat more BugsEdit
In this battle, split the team up into three parts: take Darkling, Shadowboxer and Festus through the left-most passage and use Darlking's Shadowport ability to place him behind the left-most Shadow Bug and backstab him with Mind Blast, then place Shadowboxer between the two bugs and attack, then bring Festus around and place him to the left of Shadowboxer (so that if Darkling gets attacked, he can Shadowport behind Shadowboxer and can get healed); take Gamblin' Jack or Helena (as long as one of them has more than 27 hp and deals at least 10 damage it would be fine) and bring them to fight the right-most Shadow Bug; use remaining teammates to attack from afar the remaining Shadow Bugs (try staying in the upper side of the map, so as not to attaract the attention of the second-from-the-left Shadow Bug) so that during their turn, the wounded Shadow Bugs will come upwards at the teammates and lure out the Nymph. During the next turns, use the Shadowlings and Gamblin' Jack/Helena to destroy their respecive quarries, whilst the rest of the team should try actively to destroy the Nymph (try dealing minimal damage to the Shadow Bugs, so as to keep the Nymph occupied)- Niven's Fling/Trick Shot and the Hero's Feedback/Pyro Blast should do the trick. Finally, use the entire team to kill off the last two Shadow Bugs in the centre of the map.
Battle Three: defeat the bug queen and the spriggats to escape the pitEdit
This will be, naturally, the hardest battle of the three. If you play smartly, then the Bug Queen should not be a problem to you: she doesn't actually leave her resting place, she only moves to attack, and here is the crucial bit- she attacks a 2x2 area in front of her and deals a whopping 17 damage! Thus, try to avoid placing any teammates into that area. This time, again, the easiest way is to split the team into two halves. The first half, comprising of the three Shadowlings (excluding Niven) and the Hero, should try taking on the two Shadow Bugs and a Red Spriggat on the right side of the map- one way it to use Darkling to distract the Spriggat, whilst the rest concentrate on the two Shadow Bugs (using Pyro Hail would certainly help). The second half of the team could be moved westwards and used to attack Shadow Bugs 4 and 5, whilst using them and the stone obstacle to insure that Shadow Bug 3 cannot join the foray straight away- try to use as many teammates as possible to attack one Bug and, hopefully, take it out before their turn begins. During the next few turns think through teammate positioning and kill off the initial 6 enemy units (drawing out the Red Spriggat would allow him to come under fire from the Hero as well), then retreat the team to the bottom right of the map and heal, as it's likely that the teammates who were operating in the left side of the map don't have enough health to face the second Red Spriggat, who slowly made his way down the map. Wait for the Red Spriggat to come and then attack him, whilst making sure not to come too close to the Bug Queen. Finally, send two Shadowlings to the upper left side of the map and kill the Nymph, then use any range 3 attacks available (such as Pyro Hail or Dark Vortex) to deal damage to the Bug Queen without her being able to retaliate against you. If you don't have any long-ranged attacks, then file up your teammates and let them attack her one-at-a-time, making sure there is space for them to stand back and get healed- this will probably be the faster method, as using long-ranged attacks usually costs a lot of PsP, which will take quite some time to recuperate, you can also take flying units to attack the Nymph, and the Bug Queen ( she can't hit you there.) In the end, you escape the Bug Pit and can continue your initial assignment.