- He'll invade the player in the Forest of Fallen Giants, near the Soldier's Rest bonfire.
- Iron Keep's main gate. He'll usually invade after Fencer Sharron, although sometimes he can invade first.
Armorer Dennis is a very dangerous dark spirit due to his continuous and extensive use of sorceries. He'll relentlessly run toward the player and attack, giving little chance to find an opening. If the player opts to raise a shield, he'll be prone to perform a guard break and follow with two or three slashes from his Blue Flame. Most of the time, however, he'll be casting sorceries which can cover a large area, like Soul Greatsword or Soul Vortex. If the player is far away, he'll cast Soul Spear.
Special care must be taken when he invades in the Forest of Fallen Giants, as the player will usually be at a low level when they first visit that area. Engaging him alone is not recommended until the player has leveled up and acquired better means for both attack and defense. Low-level characters should employ the help of Ruined Aflis for this fight (see below).
A good strategy is to bring a great hammer, hold it with both hands and perform a strong attack to smash him into the ground. Trying to land another hit while he's recovering is arguably recommended, as he could roll away and retaliate with a quick barrage of attacks. To ensure a hit, the player may wait for him around a corner and attack him as he closes in, then find another corner where to hide in and repeat the process until he's defeated.
Equipping armor that has high magic damage resistance, as well as wearing the Spell Quartz Ring and using miracles such as Magic Barrier can greatly reduce if not outright negate the damage that his spells deal, leaving only his physical attacks as a threat.
At Iron Keep, due to the stage's layout, a different strategy should be adopted. The player can use the walls around the main gate or the two staircases going down to evade Dennis's attacks. A good strategy is to lure him into running around one of the staircases and attack him every time he's about to reach a corner. If he casts a sorcery, the player can just drop down, making his attacks miss completely and giving them enough time to heal.
- Armorer Dennis is susceptible to the Poison, Toxic and Bleed status ailments.
- The white phantom NPC Ruined Aflis can be summoned for help just before the Forest of the Fallen Giants encounter. His summon sign is located just to the right of the bottom of the stairs leading into the dark hallway with the skeletons. It is recommended, however, that you journey ahead and dispatch the three Old Ironclad Soldiers lying in ambush atop the building first, as these can make short work of Aflis before ever even encountering Dennis. With his help as a distraction, the fight should be a breeze even at low levels.
- Burning a Bonfire Ascetic on the Soldier's Rest or the Threshold Bridge bonfires will respawn him.
- Easy kill: When Dennis spawns, run back to the first Bonfire and hold up your shield, (standing by the side of the stairs next to the Bonfire will block most of his sorceries), he will follow you, and will try to circle around you, forcing him to stand in the lava field, which quickly tears through his life. Using this trick you can defeat him without attacking even once.