Wow, this copy pasted from the wiki quite nicely.
Regulus Harassment DPS (Guide)
This guide is for a DPS Regulus that focuses on harassing enemy Demigods and killing towers quickly. It remains a good threat throughout the game and will absolutely decimate late game. It excels in tactical play and slaying demigods, but is very weak in direct combat.
Introduction
This is a harassment build based on some serious DPS punishment for anyone that even remotely comes near you. This build focuses purely on DPS and the ability to move around quickly. Early on, it's a very aggressive build, people never seem to expect a Regulus to chase them or be a threat in the beginning, more kills for you. It also completely decimates structures if they leave you alone, which is good because players will start avoiding you.
This is probably the most aggressive Regulus you will ever see. He focuses heavily on maneuverability and tactics over defensive playing. This means he will die very quickly if you make a mistake. If you are new to the game, I'd suggest a mine/snipe build, as it is much harder to kill.
Rules of this build
1) Never, ever fight a player directly early on. If they hit you, you're failing. You will most likely be the squishiest player on your team early on. A couple hits and your in trouble. The best tactic is to potshot the other player every time they try to ignore you. And run to your tower whenever they chase you. Abuse movespeed to its fullest.
2) Always have a combat potion. People target squishy players, meaning you will be getting chased and hit a lot. Potions will almost always save you, and have a tendency to get the overconfident aggressors (Like me) killed. Late game start buying artifact potions. They're a bit expensive at 1000 gold, but they usually deny your opponents kills, meaning you get your money's worth.
3) Don't harass people with priests. You're wasting mana until the priests go down.
4) Do not sacrifice yourself for a kill. Living is more important, however there is one exception, kamikazi tactics 1v1 are ok as long as a demigod does not get the kill and you do, you will gain more out of it than your opponents. However, remember your opponents might be packing a potion, and then your screwed. It's almost always better to play it safe.
5) Do not 1v1 people faster than you. It doesn't work, no matter how bad you want to kill that accursed beast player. Harass them like crazy if you've got a tower to run to though, normally you can get a good distance before they catch you.
Gameplay
Early Game (Level 1-10)
Your starting item set always: 1 Scalemail, 1 Gauntlets of Brutality, 1 Combat Health Potion. Buy a Swift Anklet as your favor item.
Level 1 is always Angelic Fury, you tag faster, meaning you can harass more. +25 damage is nice too.
Go straight to a lane flag, the early cap is much more useful than something like the experience flag in cataract. Encourage teammates to prioritize the health flag, as players will be much more vulnerable to your tactics. Camp your lane and judge your opponent. Pretty much anything but a spit beast should be harassed. (Spit beast is more painful than you are, avoid them unless there's a general with priests with you.) Do not use a potion unless it is saving you from certain death. You don't want them to think you have one, because then they won't chase you into towers if you're low.
VARIATION: Get Snipe level 1, use it to leech assists for 500 gold. I don't like to use it because normally I'm the one chasing the guy anyways, but the extra money can really help if you're unable to harass properly. Never use it to harass, it's a waste of mana.
Level 2: Sniper's Scope. Increased range makes it less likely the enemy can hit you back, and your harassing is now more effective and less risky. You can also get about one more hit in before you enter tower range. Also, by now your enemy has most likely retreated due to your efforts, so you can poke their tower a little between waves. Avoid using Angelic Fury on them for now though.
At this point, gauge your opponents and their skill. If you are up against a fellow harasser, you want to get a Narmoth's Ring (4k) ASAP, and you will find yourself quite useless until then. If you are able to successfully push them away, get a Nature's Reckoning (1.5k) and Boots of Speed (1k). I find natures is highly underestimated, but it will get you kills on heroes because they never expect the sudden 250 armor ignoring damage. And later in the game it will trigger like crazy. Once you get all these items, save for a Mage Slayer.
Remember, always harass your opponents when they aren't chasing you, just make sure you don't get in melee range. Do not be afraid to chase people into towers if they run, But do not chase them into 8+ towers, 1-2 is usually survivable. Remember though, your life is more important than killing. Don't overextend if there's even a remote chance of another demigod attacking you. This takes a lot of trial and error (Very painful error) to know when to chase and when to let them go. If you really want to you can grab level 1 snipe for leeching assists and occasionally killing those that get away, but you most likely won't have mana to spare or the time to get it off.
(Note, if you skip Enhanced Attributes you'll find yourself mana starved, deactivate Angelic Fury whenever you're not harassing a demigod or tagging. Later on this won't be much of a problem.)
Level 3: Enhanced Attributes
Level 4: Angelic Fury
Level 5: Maim or Sniper's Scope 2
Level 6: Enhanced Attributes or Sniper's Scope 2 if you don't have it.
Level 7: Angelic Fury
Level 8: Sniper's Scope 3 (At this point, towers are less risky for getting ganked, and you'll drop them very fast.)
Level 9: Enhanced Attributes or Maim if you find demigods are outrunning you still.
Level 10: Angelic Fury
Mid to Endgame (Level 11-20)
Around level 11 you should be able to afford a Mage Slayer. This is about the time when you become a devastating force with 20% lifesteal and about 400-500 base damage arrows. Save for an Ashkandor at this point (Or giants). A Regulus with an Ashkandor can drop the citidel in approximately 20-30 seconds.
As for leveling, finish off Enhanced Attributes, Sniper's Scope, and Maim if you haven't yet, focus on attributes though, it helps more than one would think. Personally I like to get Vengeance at this point cause it's fun to use. But serious people might want to max Mark of the Betrayer at the end.
Items
Regulus is very squishy. Here's a couple item sets and orders to consider. You should always get a swift anklet, speed is key when harassing.
Item Builds
Help! Help! I'm being harassed!
(Focus on attribute bonuses as well, use something like this against spit beasts, torchbearers, or maybe even queens.)
(Always) At least 1 Combat Health Potion [275 or 1k]
(S) Scalemail > (4) Nimoth Chest Armor [1500 - 320 = 1180]
(S) Gauntlets of Brutality > (5) Mage Slayer [8k - 320 = 7680]
(1) Narmoth's Ring [4k]
(2) Boots of Speed [1k]
(3) Nature's Reckoning [1.5k] > (6) Ashkandor [18000 - 1200 = 16800]
Run in fear cowards!
(Default, if everything goes according to plan you should use this)
(Always) At least 1 Combat Health Potion [275 or 1k]
(S) Scalemail
(S) Gauntlets of Brutality > (4) Mage Slayer [8k - 320 = 7680]
(1) Nature's Reckoning [1.5k] > (5) Ashkandor [18000 - 1200 = 16800]
(2) Boots of Speed [1k]
(3) Narmoth's Ring [4k]
I'm Feeling Lucky. How bout you?
(Focuses on using crits and bonus damage to catch your opponents off guard. Note that crits stack, a triple crit will probably drop someone instantly, though it's quite rare. Very satisfying to see 4000-6000 damage crits though. (1% chance)
(Always) At least 1 Combat Health Potion [275 or 1k]
(S) Scalemail > (4) Duelist's Cuirass [3k - 320 = 2680]
(S) Gauntlets of Brutality > (5) Mage Slayer [8k - 320 = 7680]
(1) Nature's Reckoning [1.5k] > (7) Ashkandor [18000 - 1200 = 16800]
(2) Boots of Speed [1k] > (6) Slayer's Wraps [3.3k - 800 = 2500]
(3) Narmoth's Ring [4k]
Other useful situational items.
Wand of speed - good for getting around and escaping ganks.
Caplock - You'll frequently be capping deeper flags, can really help your War Score if used correctly.
Teleport Scroll - Usually good to have 1 for ganking or if you know your about to be collapsed on. Your damage will quickly turn the tides of battle.
Orb of Defiance - Nice hp and armor boost, good for denying teams that love to gank you in large fights.
Combat Mana Potion - useful if you keep getting mana starved.
Totem Of Revelation - Gives a sight range boost, which may occasionally save you, it only cost 50 gold anyways.
Wyrmskin Handguards - 8% chance to slow by 15% and give 60 bonus damage, can get you kills on the more skiddish people.
Various Notes To Keep In Mind
-This build can easily be switched to a mine dps hybrid build at level 5. If dps clearly isn't going to work. Go straight Mines from here, but don't use them at all until Mines 3, you'll catch em off guard and probably get a kill out of it.
-"Tagging" Is dealing 25% damage to a unit so you will get the gold for it.
-"Ganking" or "Collapsing" is suddenly grouping up on one hero, usually with an ambush.
-"Harassing" is attacking demigods as much as possible, but only when they cannot retaliate. Usually, you hit them once and start to run towards your tower.
-If you have a potion, you can usually 1v1 any demigod standing in your own tower from any hp amount. Having low hp can be used to lure demigods into overextending, and the potion will keep you alive long enough to drop him.
-Sedna is your best friend and worst enemy. You can usually chase demigods mostly to their spawn if a sedna is around. However, make sure she can heal you, If you die, it's your fault, don't depend on heals or you'll quickly find yourself dead.
-Focusing Maim is useful if your team is frequently being outrun, always hit chasing opponents to get them off teammates. Your dps is usually enough to get them to back off, but the slow can make a huge difference.
-You are a kill hoarder, if you're getting all the kills, get citidel upgrades for your team (Currency, Tower Regen, Experience, Giants) They are more likely to get ganked than the Regulus that stays as far away as possible.
-Support heroes hate spread out damage, try to get every demigod down to about half in longer fights to make it harder for heals and shield, then focus fire and change targets every time a buff is cast. DPS is very good at this and your range will disguise the preparation. Also people who think they are being focused will not pressure as much.
-Decimate towers every time you're left alone, it allows your team to pressure easier and makes it so you can chase further. Don't let yourself be ganked though, no matter how low the tower gets.
-The most difficult hero to kill with this build is Sedna early, and Erebus late. Sedna starts to run into problems when you outlifesteal her damage, and Erebus' teleport makes him almost impossible to chase. Unclean Beast is the most dangerous, as he is usually faster than you and has spit for early game which means you have to play defensively (And rush a narmoth). Later on he has some pretty nasty damage and you should exploit your range advantage to it's fullest.
