Baron Nashor

Baron Nashor is the most powerful neutral monster on Summoner's Rift in League of Legends. His name is a tribute to Roshan, (his name being an anagram of Roshan) a monster filling a similar role in Defense of the Ancients.

It is described in-game as follows: "This is a very powerful hostile monster, approach with caution! Killing this monster will yield great monetary and magical rewards to the team, but it should not be confronted alone".

Killing the Baron gives the buff to all living champions on the team. This buff gives massively increased attack damage and ability power as well as a bonus to health and mana regeneration. When Nashor is killed, each player on the team is also granted the following:
 * 900 experience points
 * 300 gold

Lore
The Journal of Justice clarifies this about Baron Nashor :

''The many neutral monsters on the Fields of Justice are constructs inspired by real creatures from Runeterra. The Baron Nashor you see on the map is actually an incomplete facsimile of the true Baron Nashor, who is now the subject of myth and legend. The story goes that Baron Nashor was a ferocious worm that ruled the Serpentine River, which flows through Summoner’s Rift. He was such a fearsome and powerful beast that even the armies of Demacia and Noxus steered clear of the river, unwilling to chance an encounter with the Baron.''

''When Summoner’s Rift was constructed, the Baron vanished, leaving no conclusive evidence as to where he went or why he left in the first place. Obviously the rumor-mill has churned out many explanations, but all we know for sure is that the Senior Arcane Architect for the Summoner’s Rift arena was said to have crafted the version you see today from no more than a molted scale and interviews with those who had seen the beast and lived.''

Abilities


Baron Nashor has four abilities. While they are not revealed in-game on a death screen, their debuffs and animations are visible and distinctive.

Wrath of the Ancients deals magic damage and applies a debuff which increases magic damage taken. It stacks up to ten times. This increase in damage is applied to the damage taken before magic resistance, and while functioning in a similar manner to magic resistance reduction, it is not the same thing.

Voracious Corrosion deals physical damage and applies a non-stacking debuff that greatly reduces attack damage. This is a major issue for AD-based champions trying to solo him.

His third ability, Sweeping Blow, knocks all champions away from the Baron by a set range. This range is equivalent to the distance between the Baron and the entrance to his locale.

Lastly his fourth ability is a knockup and slow similar to. A green puddle of bubbling fluid shows on the ground before the spell hits, making it relatively easy to spot and subsequently dodge it.

Baron Nashor will usually start with Wrath of the Ancients. He will continue using Wrath of the Ancients unless he feels you are doing too much physical damage, at which point he will start using Voracious Corrosion to keep its debuff on you while alternating with Wrath for damage. He will mix in the knockback and knockup moderately often throughout the fight.

Gameplay
Baron Nashor is immune to all forms of Crowd Control. Killing him should not be attempted until mid or late game.
 * Baron Nashor is often a key objective in competitive games, probably because of its massive gold bonus (+300g/player) and global buff.
 * Soloing Baron Nashor is not recommended. This is due in part to his large health pool and in part to the debuffs he will apply to your champion. The key to soloing Baron Nashor (besides a mandatory high level of DPS ) is to make sure he can't keep his debuffs on you - a full ten stacks of Wrath of the Ancients will increase his DPS to the point at which he can melt even full-build tanks.
 * Killing Baron with a team is fairly simple. Baron primarily attacks the target closest to him so you can distribute damage by moving characters closer and further away from him.
 * Tips and Interesting Strategies you should note before "attempting to Baron":
 * The enemy team likely will have a ward placed to see when you initiate. If you do not destroy these wards with the use of a Vision Ward or Oracle's Elixir, they may be able to assult your team while you are weakened by Baron and subsequently steal the buff, which will likely result in a game-deciding push for their team.
 * Baron Nashor's buff is given to the team that deals the killing blow on Baron. This mechanic means that even if one team is incapable of directly fighting the enemy team, a jungler with the Smite summoner spell can possibly swoop in and steal the Baron with a well timed smite. This is almost definitely a suicide mission and is an extremely high risk maneuver. However, successfully stealing Baron can turn the tide of a game dramatically.
 * When Baron dies, the buff is only granted to those team members who are currently alive. Dead team members will respawn without the buff. Furthermore, this buff is the only buff in Summoner's Rift that does not transfer via kills. If a champion is killed with this buff, the buff is destroyed and cannot be taken again until Baron Nashor respawns.

Trivia
During the 2010 Snowdown Showdown, Baron Nashor wore three santa hats, one for each of his three faces.