Black Knight

Starting Out

You need to choose your choice from the beginning, especially with BK. Training stats you should increase whenever you get the chance are Strength, Agility, Reputation and Toughness. Any other stat should be equal, only increasing when you need to use gear different gear. 

When you get to level 20 and have the old Market, you should look for the following gear to begin your BK tattoo:

Hard Hat of Adrenaline
Vest of Adrenaline
Amulet of Strength
Ring of Youth x2
Light Shorts of the Rouge/Smuggler
Murderous Mace

The (+5) effects of each of these items will be enough to use level 1 tattoos. 

Further On

Your gear should advance with your character. And by buying better more reliable gear, you can fully develop your character.

Battle Helmet of Adrenaline
Field Vest of Caligula/Orchid/Cobra/Assassin
Chain of Levitation(Titanium Prefix would be a bonus)
Ring of Youthx2(Titanium again)
Shorts of the Scout
Leg(if your act II) Murderous two handed sword of the basilisk.

This next gear will cost far too much. But it's something to work towards:

Assault Helmet of Adrenaline
Field Vest of the Deathsower
Titanium Chain of Levitation
Titanium Signet of Youth
Titanium Ring of Youth
Elvish Shorts of Smuggler(P+1 for extra defence)
Legendary Murderous Scythe of the Basilisk

Tattoo

Required weapon: Two-handed melee weapon
Tattoo requirements do not apply to the last tattoo in the path (the experience tattoo):
LEVEL 1 : helmet defence min 7, armour defence min 11, pants defence min 7
LEVEL 2 : helmet defence min 14, armour defence min 22, pants defence min 14
LEVEL 3 : helmet defence min 21, armour defence min 30, pants defence min 21
LEVEL 4 : helmet defence min 28, armour defence min 46, pants defence min 28
LEVEL 5 : helmet defence min 35, armour defence min 70, pants defence min 35
Heart of Darkness
LEVEL 1: 1000 PoP, 1 bloodstone
Traits: Chance to hit with all weapons +12 
LEVEL 2: 2000 PoP, 1 heartstone
Traits: Chance to hit with all weapons +24 
LEVEL 3: 3000 PoP, 1 lifestone
Traits: Chance to hit with all weapons +48 
LEVEL 4: 4000 PoP, 1 mergestone
Traits: Chance to hit with all weapons +60 
LEVEL 5: 5000 PoP, 1 soulstone
Traits: Chance to hit with all weapons +75 
Power of Faith
LEVEL 1: 1000 PoP, 1 bloodstone
Traits: chance for critical strike +5 %
LEVEL 2: 2000 PoP, 1 heartstone
Traits: chance for critical strike +10 %
LEVEL 3: 3000 PoP, 1 lifestone
Traits: chance for critical strike +15 %
LEVEL 4: 4000 PoP, 1 mergestone
Traits: chance for critical strike +22 %
LEVEL 5: 5000 PoP, 1 soulstone
Traits: chance for critical strike +30 %
Double strike
LEVEL 1: 4500 PoP, 2 bloodstones
Traits : LUCK +1
LEVEL 2: 9000 PoP, 2 heartstones
Traits : LUCK +2
LEVEL 3: 13500 PoP, 2 lifestones
Traits : LUCK +2, additional 1 attacks with every weapon
LEVEL 4: 18000 PoP, 2 mergestones
Traits : LUCK +4, additional 1 attacks with every weapon, HP +5 %
LEVEL 5: 22500 PoP, 2 soulstones
Traits : LUCK +6, additional 1 attacks with every weapon. HP +10 %
Apprentice of the Dark Side
LEVEL 1: 4500 PoP, 2 bloodstones
Traits : experience +4 % (aura*)
LEVEL 2: 9000 PoP, 2 heartstones
Traits : experience +8 % (aura*)
LEVEL 3: 13500 PoP, 2 lifestones
Traits : experience +12 % (aura*)
LEVEL 4: 18000 PoP, 2 mergestones
Traits : experience +16 % (aura*)
LEVEL 5: 22500 PoP, 2 soulstones
Traits : experience +24 % (aura*)

If you want extra attacks as a Black Knight, make a slight change to the last set regarding armour.

Field vest of Speed
It allows you to use level 5 tattoos and gives you 2 extra attacks at good + 5 onwards.