Devil May Cry 4 - Mission 14: Forest of Ruin
You'll encounter a new enemy a short ways down the path known as Fault. These guys are more of an annoyance than anything because all they'll is try to trap you in their mouths, which doesn't do any damage. If they do succeed, however, you're in for a bit of an annoyance because you are then brought to the Ruined Lowlands where you must defeat the enemies there to spawn an exit seal. The enemies encountered in the lowlands could very well be those annoying Chimera-infected Assaults, so try your best to avoid being sent there. When you use the seal to exit the lowlands, you'll end up back at the start of the area, which can be quite irritating.
With that said, the Faults are easy enough to avoid; keep an eye out for the shape that appears just before they are about to emerge and jump up into the air or move to the side to avoid getting sucked in. Destroy the Scarecrows at the far end of the area -- watching out for Faults all the while -- and use the exit to proceed to the next area.
This area is occupied by Mephisto, so switch to the shotgun and start removing their cloaks. The Faults will follow you around for the rest of this mission, so remain vigilant. Defeat the Mephisto and the Faust that then spawns and leave the area using the exit at in the northwest corner.
Ancient Plaza/Windswept Valley
Clear out the Assaults here to remove the red mesh covering the entrance and the exit, then head through the exit at the other end of the area.
Move forward until a group of Chimera-infected, or soon-to-be-infected, Scarecrows and Assaults spawns. The Faults are much more aggressive here, so you'll likely have to spend the majority of this skirmish airborne. Shower the enemies below with shotgun fire on your way down and then commence the slashing until you're forced up into the air again by an emerging Fault.
After the fight, hop up the ledges at the northwest end of the valley and use the exit at the top to leave the area.
Attack the Red Orb cluster (Shredder seems to work quite well) until it shatters to receive a large amount of Red Orbs. The Royal Blocker secret mission parchment is attached to the ruins here; you had to pass it by while playing as Nero due to lack of the Royal Guard style. Attempt it if you wish, otherwise head through the tunnel to reach Foris Falls and clear the mission.
Red Orb Cluster
Secret Mission 08