Let's get one thing straight here. This is not your standard Nautilus Guide. Hell it's not even close to Meta. This is what I play for fun. I don't claim it's the most effective way to play him, because I am pretty sure it isn't. I know there are other apcs that can do his job better, but I don't care. I know he was meant to be built tanky, but I don't care. Just try it once or twice. If by the end of the experience bursting down an enemy from 100 to 0 doesn't satisfy you, then hey at least you tried. This build focuses almost exclusively on ap/as on hit and builds no health or armor, with very little MR. Do not expect to play like you normally would with nautilus. This requires learning to play him all over again as a squishy ap. And I wouldn't have it any other way.

Lich Bane> Wit's End> Nashor's Tooth> DFG> Void Staff With Sorc. Boots Furor when you feel like it. If you prefer more CDR go for Ionian boots, And if you want to have some tankiness Ninja tabi/and mercury treads depending on the enemy composition.

Lich bane's active synergizes with your hit and run style and passive. It also provides a little move speed and ap to help your damage and mana which helps in the early game.

Wit's End provides some defense in the form of mr to you, mr reduction to enemies, and Attack speed which helps you get more shield and Nashor's procs.

Nashor's Tooth's passive and ap helps your basic attacks hit a little harder, but the cdr and attack speed really help nautilus due to his long cooldowns and help him proc his shield and Wit's end a little faster.

DFG CDR helps with Nautilus' long cooldowns, and the ap and active really help you burst down targets.

Void Staff for more damage via ap and magic pen

Passive: Snares enemies and deals bonus physical damage. Use this to last hit and harass if possible. Along with the 3 on hit items and your shield this will hit like a truck.

Q: Used to initiate and escape from fights. Will deal decent damage later in the game to aid your combo. It also disrupts enemies so it is useful for keeping enemies from attacking you or stopping them from casting.

W: Used to clear waves or deal damage to enemy champions in the form of an aoe dot on basic attack and absorb harass/win trades. You build attack speed to get more of your shield's on hit procs. These procs along with the items you build will hit hard. Use these while your skills are on cooldown to keep up the pain. Note that you can only proc the bonus damage on basic attacks while your shield is up, you have been warned. Though if all goes to plan, you should CC them so hard they won't be able to break your shield! (Or they ran way, either works)

E: Used to Harass and farm lane. Will become a great asset to your combo. If you can hit all 3 waves this will hurt ALOT. Otherwise it will still hurt, just not as much.

R: Used to finish/initiate fights and to cc enemy targets. Will deal a large amount of burst damage if used for your combo.

Nautilus is weak against champions with long range/good harass. You may also have a hard time against champions with alot of cc or kiting potential. Try to farm passively or roam if you are facing one of these.

That said, he is one of the best counters to Fizz I have ever seen and would likely do well against melee champions with poor trading potential or mages without a good form of cc. Trade with these often as your shield and burst will often leave you winning small trades, though you may run low on mana in the early game.

Farm minion waves with e+w and your passive will help you last hit minions.

Since this build is not as tanky as most other Nautilus builds, try to stay behind your team until they catch someone or try to q an enemy that wandered a bit too far away from his team, allowing your team to do most of the damage. Hit him with a small combo and fall back while you wait for cds. If you have your ultimate don't hesitate to use it on that carry in the back of the enemy team not only to hurt them and cc them but also to deal damage to anybody in front of them. If an enemy is about to get away, flash ulting can secure the kill for your team. This Nautilus build depends on having a team that can manage to hold off a 4v5 while you focus on catching the runners, though he is more useful trying to find an enemy alone, bursting him down, and using the number advantage to help your team push objectives or prevent teamfights.

Skirmish Sequences-

If close to enemy:
W>Basic Attack>E>Basic Attack>Flee

If far from enemy:
Q>W>Basic Attack>E>Basic Attack>Flee

Finisher(Enemy is behind Minions):
R>Flash>W>Basic Attack>E>Basic Attack>Ignite>Q

Finisher (Enemy is in the open):
Q>W>Basic Attack>E>Basic Attack>Ignite>R (Flash if necessary)

Late Game Full Combo-

Enemy walks into your bush:
DFG>W>Basic Attack>E>Basic Attack>Q>Basic Attack>Ignite>R (Flash if necessary)

Enemy is in the open:
DFG>Q>W>Basic Attack>E>Basic Attack>Ignite>R (Flash If necessary)

(In team fights use the Skirmish Sequences)

*Since you are using 3 on hit items, try to mix in basic attacks as often as possible while still cc'ing the enemy*