Soul Level: 152
Recommended Class: Swordsman
VGR: 40 (This will give you a steady HP pool without experiencing much of a drop off)
END: 20 (The soft cap for stamina is 20, after that it becomes expensive maintaining a higher stamina)
VIT: 30 (Getting to 29 for the equipment load is essential if you want to use heavier armour, I went with 30 for a nice even number.)
ATN: 10 (This allows you one slot for magic)
STR: 20 (Soft cap for strength, allows some versatility for weapons and shields)
DEX: 60 (While 40 Dex is essential for this build, I find that boosting Dex to 60 helps with your bleed and poison bonuses, which is necessary here)
ADP: 10 (It isn't necessary to raise your ADP for this build, but I found that a couple extra points is helpful)
INT: 10 (This allows you to cast basic spells)
FTH: 5 (Leave at default. Faith is unecessary for the mercenary, you rely on yourself and not a higher power right?!)
While the specifics aren't important, it is essential that you take advantage of your higher DEX and use weapons with large DEX modifiers. It's also important to take advantage of your bleed and poison bonuses. Typically, your ideal loadout should be two curved swords, a bow, a poisoned whip, and a light shield. If you feel more comfortable using a two hander with a large DEX bonus feel free, but I would suggest having a one handed poison or bleed weapon as a backup. Keep poisoned throwing knives in your arsenal.
Right: Falchion +10 Hunter's Blackbow +10 Sorcerer's Staff
Left: Falchion +10 Spotted Whip +5 Llewellyn Shield
Armour is largely personal preference. If you want to wear heavier armour, go for it. If you prefer lighter gear, feel free. The only requirement is to maintain your roll, that is your biggest defense. Why block what you can dodge? I try to keep my weight under 50% for increased stamina regeneration and a faster roll. With 29 VIT you have flexibility and can use mostly heavy armour if you choose to do so, but be mindful of your weapon loadout. Do not sacrifice your versatile weaponry for a few extra points of defense, you have enough health and mobility to compensate.
Head: Thief Mask +10 or Vengarl's Helm +5
Chest: Throne Watcher Armour +5 (I like the higher magic defense) or Vengarl's Armour +5
Hands: Drangleic Gauntlets +5 or Shadow Guantlets +10
Legs: Drangleic Leggings +5 or Vengarl's Leggings
I am a little more particular about rings, while you're certainly able to experiment on your own, I feel that the proper Drangleic Mercenary focuses on wittling down their opponent while maintaining both a high physical attack and defense in case that doesn't work. If you are facing hordes of enemies, you can use whatever you feel will keep you alive, but ideally you should avoid being hit completely. Use your rings in proper balance, try to set yourself up in case of an error while taking advantage of your setup in the event that everything goes according to plan.
Rings: Ring of Blades +1, Red Tearstone Ring, Spell Quartz Ring+2, Ring of Steel Protection +1, Life Ring+1, Second Dragon Ring, Crest of Blood, Ratcrest Ring
Spell use will never be your priority with this build, however I do think you should take advantage of Magic Weapon to increase your attack without relying on items. You can also use Simpleton's Spice and lower the requirements of Homing Soulmass if you find enough. Other than that, I don't think you should worry about spells. Focus on your swordplay and mastering your rolls, poison and bleed the enemy out. Get a couple Sorceries or Pyromancies if you prefer, but don't bother with Miracles or Hexes. However, if you decide to branch out try focusing more on lingering status effects or weapon buffs, which don't scale with int.
Sorcery: Homing Soulmass, Magic Weapon, Chameleon
Hex: Dark Fog, Dark Weapon
Pyromancy: Poison Mist, Acid Surge, Flame Weapon
Miracles: Sunlight Blade
Strengths: Your biggest strength is your aggressive attacks. Your high DEX and moderate STR in conjunction with the status effects from your weapons makes you a ferocious melee attacker. You can utilize your bow to do substantial damage as well, provided you time your shots. You will have speed and time on your side, provided you properly poison enemies and dodge attacks. Your fast attacks and status effects will keep your enemies on the defense, and your moderate reach will allow you to play close or medium range with some versatility. You have the defense and health to take hits, but you have the flexibility to avoid them entirely. You are not a heavy tank, but you aren't a glass cannon either. Use your high damage output to charge and destroy magic users, use your speed and status effects to outmaneuver tanks. Against tanks with high Adaptibility, you will still be able to take advantage of your high damage and speed, just be patient and time your rolls. Lure them into an attack and work your way behind them, or let them drain their stamina and counter. You have a high versatility with your weapons, you can keep everyone on their toes by switching between sword/shield, dual swords, whips, bow. Keep the enemy on the defensive and you can widdle them down 90% of the time, make them fear lowering their shield or opening up for an attack. Keep mages close, they aren't a threat if they don't have time to use their spells. Use magic weapon to take advantage of melee fighters who lack proper magical defense.
Weaknesses: Let's be honest with ourselves, there is no such thing as a perfect build. Everyone is going to be better in some way. Your biggest and most glaring weakness is going to be your lack of offensive spells. If you set yourself up properly, you can avoid damage from fire, poison, curse, or magic provided you know what you're facing in advance, though that is rarely the case. If you don't know, try to anticipate. I typically keep my magic defense higher as the biggest threat for me is longer ranges. Since pyromancy has more close range spells, it is easier to counter (though devastating if you fail) A low Adaptability means you may suffer the same fate that you're trying to inflict on others, fortunately your high attack and moderate defense can often counter people who try to poison you to death. The last flaw is timing. You have several weapons and if you're caught with the wrong one at the wrong time it can lead to a quick departure, make sure you work on your timing. Keep your weapons ready for each scenario and keep rolling. You're faster than almost everyone else, whether you're smarter or not is debatable.