Darmanitan

Darmanitan's high ATK stat and access to a powerful relevant moveset puts it near the top of the non-shadow/non-mega Fire Type DPS list. However, it's a rather difficult Pokemon to obtain outside of events. Its performance is comparable to that of Reshiram's, however Darmanitan's bulk causes it to faint much sooner, making it a slight downgrade in terms of overall performance. That doesn't mean Darmanitan is a bad Pokemon though. 

Best PvE Offensive Moveset

• Fire Fang is superior to Incinerate in PvE offense. 
• Tackle is bad, TM this. 
• Overheat enables Darmanitan to fulfill its Fire-type role and is recommended. 
• Focus Blast can be a decent downgrade option if lacking TMs. 
• Rock Slide is more flexible as a 2-bar move, but only synergizes well against Ice-type Pokemon.
• Psychic is better suited for Psychic-type attackers. 

Best PvE Defensive Moveset

• Incinerate is the best on defense due to its incredible base power. 
• Fire Fang has less than half the base power of Incinerate, making it considerably worse on defense. 
• Tackle is bad on defense, just like how it's bad on offense. 
• Psychic as a 2-bar move can be used frequently, and provides strong neutral damage. 
• Rock Slide is a slightly worse option in both damage and timing, but still good for its wide coverage.
• Overheat as a 1-bar move might not be accessible before Darmanitan faints.
• Focus Blast provides the best coverage, but is also the slowest and easiest to dodge. 

Incinerate is generally recommended for its considerably faster energy generation compared to Fire Fang, but the latter offers slightly more damage output. Tackle is useless. 

Rock Slide is an efficient charge move and provides valuable coverage. Overheat costs a moderate 55 energy and has the potential to deal massive damage if unshielded, but a -2 ATK self-debuff makes it risky to use. Psychic costs the same amount of energy, but its coverage is less useful in most formats. Focus Blast is often too expensive to use energy-wise, but its coverage and high damage could be significant if unshielded.