One of the great things about Fairy Tail is how iterative each character's magic abilities are. From a few bread-and-butter unique attacks to an arsenal of massive, world-annihilating magic, the protagonists are constantly improving and combining old moves to best the next "big bad." No one proves that better than Natsu Dragneel, Fairy Tail's main character.
The only human capable of using Fire Dragon Slayer Magic, Natsu is debatably the strongest wizard in the series by the end. The majority of his moves are fire-based, often an augmentation of his physical attacks, but he eventually develops his Second Origin, allowing him to use Lightning Dragon Slayer Magic as well.
10 Crimson Lotus: Exploding Flame Blade
With such an extensive array of powerful magic (that sometimes powers up or down due to plot necessity), it can be difficult to compare the relative strength of his various moves. A strong indicator used in this ranking is the relative strength of the enemy the attacks took down and, to a lesser extent, the lore significance and difficulty of the magic in question. Even Natsu's tenth-strongest attack is unthinkably powerful compared to most characters. Crimson Lotus: Exploding Flame Blade, an advanced Dragon Slayer technique, is a spinning, long-range fire attack that expands on his Crimson Lotus series of Secret Arts. This move is historically notable because it previously pushed Gildarts back and beat out Sting and Rogue's Unison Raid.
9 Dragon God's Brilliant Flame
It seems crazy to put this move so far down the list, but in reality, that's a testament to the strength of the remaining entries. Dragon God's Brilliant Flame was a one-off, improvised attack Natsu used to end his battle with Zancrow, one of the Seven Kin of Purgatory. The move combined Natsu's standard Fire Dragon's Brilliant Flame with the Fire God Flames he absorbed from his opponent. The importance of this kind of magic is, well, that it shouldn't have even been possible. Zancrow himself explains to Natsu that the flames of a Fire God Slayer can't be absorbed like normal fire, making it possible to literally fight fire with fire against Natsu. But as usual, Natsu found a way, and as a result, created a unique blend of two of the strongest known magic variants in Fairy Tail. No biggie.
8 Planetary Flames: Exploding Flame Blade
Another one-off dependent on energy absorption, but that's just Natsu's style, isn't it? Planetary Flames: Exploding Flame Blade is an improved version of the previous-mentioned Crimson Lotus: Exploding Flame Blade that uses power gained from the Celestial Spirit Beast, the Eclipse version of the Celestial Spirit King.
Similar to its weaker version, the attack consists of throwing spirals of fire with the addition of some sparkles and explosions on impact. Like many of the arc-ending final moves on this list, Planetary Flames: Exploding Flame Blade is a resourceful magic attack that takes out what is essentially a powered-up version of the strongest Celestial Spirit.
7 Fire Dragon King Mode
Since Fairy Tail characters are kind enough to scream the names of their attacks as they use them, it's easy to keep track of them and theory-craft what comes next. With this in mind, it was hard not to crack a smile when Natsu debuted his new magic, named after his foster father, Fire Dragon King Igneel. Honed by nearly a year of training following Igneel's death, this evolution of Dragon Slayer magic is crazy strong, even for Natsu. If every Fire Dragon King move was included in this list individually, it would take up a lot of entries, so leave it at this—this late-game mode let Natsu outclass nearly everyone in the series, giving him the strength to beat a Spriggan 12 member in one shot.
6 E.N.D. Curse Mode
It was probably a shock for fans when the fabled demon E.N.D., destined to defeat his master, Zeref, turned out to be none other than Natsu. Whipped into a frenzy by the enlarged demon energy inside of him, Natsu adopted a more demonic appearance in this form. Utterly compelled to kill Zeref, Natsu went toe-to-toe with Gray for confronting him about his identity and stalling his mission. There weren't any particular new moves that emerged in this mode, but given that it was at least on-par with Gray's new Demon Slayer powers, it's still noteworthy. Luckily, Erza stopped the battle, and we probably won't be seeing any E.N.D. powers again.
5 Fire Dragon King's Demolition Fist
There is one Fire Dragon King move that deserves special recognition and a higher ranking than the rest, and that's the Demolition Fist. This attack makes the cut for one reason: Natsu used it to one-shot a god. Things seemed pretty desperate for the Fiore forces when an Alvarez wizard summoned Ikusa-Tsunagi, one of the Eighteen Battle Gods. Thanks to Natsu's new Fire Dragon King's Demolition Fist move, though, Ikusa-Tsunagi didn't stick around. With one massive, flaming punch, the so-called god was sent packing moments after being summoned. To slay a god without God Slayer Magic and only place fifth-best, the top moves really have to be something.
4 Igneel’s Tattoo
The epitome of Fire Dragon King Magic, Igneel's tattoo was a final gift entrusted to Natsu upon his foster father's death. Kept bandaged before its first and final use, Natsu describes the power as a one-use solution to beat Zeref. When finally unleashed, it seems to be just that, but its single use is wasted when Happy pulls Natsu away, knowing that Zeref's death would end Natsu's life as well. Despite its undoubted strength, the fact that Happy came away with only a few burns prevents this move from being ranked higher (although it's ultimately pretty lucky for Natsu and Happy).
3 Dragon Force
Not to be confused with the metal band, Dragon Force is the true ultimate ability of any Dragon Slayer. Why doesn't it rank number one? We'll get there. Along with the standard magical power-up, this form transforms its user into a more dragon-like appearance. Natsu pulls off this ludicrously strong mode several times throughout the series using absorbed energy such as Etherion and Jellal's Flame of Rebuke.
Near the end of the series, Natsu becomes the first Dragon Slayer to achieve Dragon Force without the consumption of additional magical energy. Several other Dragon Slayers, including Sting, Rogue, and Wendy manage to pull off this state as well.
2 Hidden Fire Form: Crimson Lotus: Phoenix Blade
With that many colons in the name, it has to be strong, right? This shiny, yellow, flaming headbutt uses Dragon Force to inflict massive damage. Natsu uses this attack several times, notably in his battles with Zero and (more importantly) Mard Gear. Besides Acnologia, Zeref, and Natsu himself, Mard Gear of the Tartaros guild could be considered one of the strongest wizards in the whole series. Although the attack doesn't finish him off, the fact that Crimson Lotus: Phoenix Blade deals such a decisive blow to Tartaros' leader earns it a high spot on the list. If limited-use moves were excluded, this would likely be in the number one spot.
1 Multi Dragon Force
There's no denying it—the final attack used to defeat the final, strongest villain in Fairy Tail has to be the strongest move, period. There isn't any real official name for it, but during the final confrontation with Acnologia, Wendy enchants Natsu with the power of all seven Dragon Slayers. Using the borrowed power, plus Dragon Force and his usual brand of punching stuff, Natsu destroys the "invincible" dragon's spirit form. In tandem with the rest of Fiore's assault on Acnologia's physical form, the last threat of Fairy Tail is vanquished for good. In some ways, Natsu's final attack could be considered an affirmation of the bonds he made throughout the series and the trust he earned as a steadfast friend and fearsome Dragon Slayer.