Vegnagun's Leg is a boss in Final Fantasy X-2. It is the second in a series of battles with Vegnagun at the end of the game. Leblanc, Logos, and Ormi attempt to take it out, but are defeated, leaving YRP to defeat it on their own.
The party will face the torso next.
The Red Node casts offensive magic, the Yellow Node casts buffer spells on the leg and status magic on the party, and the Green Node casts recovery magic, such as Regen and Cura, on the leg. The Nodes do not have to be destroyed to beat the leg. The Nodes change color ever so often, which leads to different kind of magic being cast. The player can make them change by targeting them with any kind of offensive magic or a dressphere that wields a gun.
An effective party formation would be two Dark Knights and a White Mage/Alchemist. It is useful to start the battle by buffing the party until each member has at least Protect and Haste. Haste isn't available to a White Mage, but it is possible to inflict this upon the party or an individual by use of a Chocobo Wing or Chocobo Feather. Chocobo Wings are created via the Alchemist's Mix ability by combining two Chocobo Feathers.
The party should cast Reflect on the leg to bounce any buffer or restoration spells to the player party. Casting Reflect on the player party will bounce any spells cast at them back to the Leg, keeping the nodes in a state of perpetual change.
With Reflect in place the party won't have to worry about offensive magic and the main concern will be to prepare for the leg's Vita Brevis attack, which does powerful physical damage to the entire party. The Dark Knights should be using Darkness.