The Dark Lord is, arguably, the strongest boss in the entire Find Mii series, possessing 200 total HP (250 in the Secret Quest), is immune to any type of magic, and, not unlike the Ultimate Ghost, can spew Level Down Gas to reduce the heroes' levels.
Find Mii II
Although absent in the original Find Mii, the Dark Lord makes his official debut in the sequal, swooping down to grab the Monarch with its tail once the Ultimate Ghost has been defeated. Flying up to the Sky Tower of the Castle of Darkness, the Monarch immediately recognizes the beast, explaining his intentions to swallow up all light in the world, and cover it in darkness. Following the explanation, the Dark Lord immediately attacks the heroes. As stated above, the Dark Lord is one of the hardest bosses in the entire Find Mii series, having the ability to spew level down gas and being immune to all types of offensive magic. Still, the heroes prevail, and the Dark Lord flashes between several colors before exploding, destroying his very existance.
He reappears in the Secret Quest, although now under the analysis of the Dark Emperor. The strategy to defeating him remains, except he now possesses 250 HP, compared to his initial 200.
Super Smash Bros for Nintendo 3DS/Wii U
The Dark Lord appears in Super Smash Bros for Nintendo 3DS/Wii U in the Find Mii stage, acting as a stage obsticle.
In contrast to typical dark lords, the Dark Lord appears as a large, orange (green as Dark Emperor) dragon with a frilled head, dissembodied, clawed hands, yellow (red as Dark Emperor) eyes, a short tail, and two large wings draping his back.
Like many characters in the Find Mii series, the Dark Lord appears too brief for his personality to be explored in deph. What can be gathered, however, depicts him as a malevolant creature. True to his name, he intends to spread darkness to all corners of the earth, implying that he despises light.