Nautilus
Pros:
He is an excellent CC master with his Shield spell also with his Riptide
He can counter some of the trickiest Champions on LOL with his passive Such as Master Yi
He as excellent skill base damage even with out any ap
He is extremely tanky when got the correct items
He can escape from ganks with his Q spell or catch up with them
Con:
He have very slow attack speed this could cause some problems when trying to active his passive on a moving target
Between lvl 1-5 His shield spell has a very very long cool down which may cause some problems early game against aggressive champions

For summoner's spell I like to use Ghost combined with Exhaust, Teleport or Heal.
The reason for ghost is because nautilus have close ranged spells Such as his titan's wrath and his riptide, these skills require nautilus to be close or next to the enemy to be effective and to maximize the effectiveness of riptide you should cause this spell when a lot of enemy is around you hitting all of them with every single riptide and ghost will allow you to catch up to a running enemy to slow and deal heavy damage to them with riptide as well as his passive.

The reason for Teleport is because nautilus is very very slow at early game Teleport will allow him to recall get his philosopher's stone but at the same time not losing any tower or much CS to the enemy so if you are soloing top or being a support tank bottom Teleport is a great summoner spell to have and its also very useful in late games.
But if you rather use Exhaust or Heal to assist your team they are still very good summoner spell's to have.
Please remember this guild is for support tank and I think this build for nautilus is one of the best and I highly disagree with AP nautilus because I believe nautilus have so much damage from his base skills I dont think Ap will be needed at all so I dont recommend ignite on nautilus at all its a waste of a summoner spell space having ignite on nautilus.

Try avoiding Ap carry build on nautilus because Ap does not scale his shield hp. His is a very important factor during team fights and sustainability.

The reason for this is because nautilus's skills are heavily based on going in to enemies and to CC them absorbing damage from towers and other team to enable the team to feed on weaker targets.
This means he shield will be the main spell for nautilus, building Ap on nautilus is a very bad idea because even if you get rod of ages or Rylai's Crystal Scepter yes they give you Ap Yes they give you good HP but you got to think titan's wrath has a very high cooldown even at lvl 18 the cooldown of titan's wrath is 18 sec that's a very very long cooldown for a main spell + on top of that you are building Ap your defe will be low so that shield will just get burst down in no time, if the shield is down and so will the area DOT damage and I believe one of the scariest thing about nautilus is that awesome area DOT damage from his shield and also those two items is very good but if you are not fed those two item cost about 3000 gold each and where as Ageis of legion cost 1900, Randuni's omen cost 3000, Spirit Visage cost 1550 and they have multi stat but will less gold giving defe and Cooldown.

So just to concentrate the thoughts:
Nautilus's main skill is Titan's wrath so building HP and cooldown reduction is very highly recommended
Nautilus is not a damage dealer because his skills require you to be next to the enemies to deal damage this means if you dont have high defe you will get killed by their team when you jump in with your Q or your ult
Try not to stay in fight for too long if your enemy can deal good damage on you because you have poor defe or what ever try to walk away from the battle but stay close and enter the batter again when your shield is up. This is why cooldown reduction is important for nautilus.

To start the game off I highly recommend buying regrowth pendant and 1 health potion or 1 mana potion. The reason for this is because The regrowth pendant is needed to make the philosopher's stone, as phreak said in his champion spotlight one you have philosopher's stone the amount of mana regen will be enough to sustain numbers of team fights before requiring to recall also the gold per sec from this item is very very useful because you are playing as Tank so you will get less kills or CS.

After philosopher's stone you should rush speed boots because you will need speed to catch up and finish of enemies. depending on the types of enemies you can choose ever ninja tabi or mercury's treads

after buying boots you should analyze your game and decide on wherever getting hearts of gold if your team is doing well or get ageis of the legion for team support, HP and some sweet defe aura.
Ageis of legion should be a main item for nautilus because of the awesome aura which provide defence for your team mates while you are tanking the enemies damage so Aegis of legion is a must have item for nautilus

After getting Agies of legions combined with your runes you should have around about 110 magic resist and once again you should analyze your match and decide on ever more armor or more magic resist. If you need armor you should get Glacial shield, this item gives armor, mana and most importantly Colddown reduction. Cooldown reduction is a very important stat for nautilus decreasing the cooldown on your shield and other skills could mean the difference between wining the game or losing the game. This is because you are the heart of your team once you fall your team will be wide open from enemy attacks.

After these main items you could choose what items you want to get adapted to your game, some other great items that is great for nautilus is Sunfire cape, Abbssal scepter or any other support items. But remember try to avoid items that doesn't give any hp because Hp is very important in scaling your shield

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