Weapon
#1- Eth Reaper's Toll- +190-240% Enhanced Damage, Ignore Target's Defense, Adds 4-44 Cold Damage, 11-15% Life Stolen Per Hit, 33% Deadly Strike, 33% Chance To Cast Level 1 Decrepify On Striking, Requirements -25%- Simply the most vicious merc weapon in the game. High %ED, Great %LL, cold damage to debilitate the enemies further, 33% deadly strike (!) and most powerful trait - 33% CTC to the most horrible of curses - Decrepify, making the mob lose 50% physical resistance (removes Physical Immunity as well), and lose 50% mobility. Socket with 15/40.
#2- Eth Tomb Reaver- +200-280% Enhanced Damage (varies), +150-230% Damage To Undead (varies), +60% Increased Attack Speed, +250-350 To Attack Rating Against Undead (varies), All Resistances +30-50 (varies), 10% Reanimate As: Returned, +10-14 Life After Each Kill (varies). Socket with 15/40's.
#3- Eth Hone Sundan- +160-200% Enhanced Damage (varies), Adds 20-40 Damage, 45% Chance of Crushing Blow, Repairs 1 Durability In 10 Seconds, Socketed (3). Massive %CB so I decided putting it in with the "killer" weapons. Experienced it myself, it's worth its place here. Intertwined with Guillaume's Face makes your mercenary have a minimum of 80% Crushing Blow, with 3 sockets (+1 helm socket- 4 sockets) to spare! Socket with 15/40's.
Helm
#1- Guillaume's Face- Hands down the best helm for a "killer" type merc. Nothing outweighs these stats: 30% FHR, 35% Crushing Blow, 15% Deadly Strike, +15 Strength. Socket with 15/40.
#2- Giant Skull- The Knock Back helm, perfect for warding off approaching enemies. Can have up to 2 sockets, 35 strength, 320 defense and 10% Crushing Blow. Socket with 15/40's.
Armor
#1- Treachery Runeword- 5% Chance to Cast slvl 15 Fade when Struck, +45% Increased Attack Speed, +20% Faster Hit Recovery, Resist Cold +30%. The IAS here will help reach the IAS breakpoint with ease. Fade is also great %CTC.
#2- Fortitude Runeword- The "off-damage" armor. +300% Enhanced Damage, +200% Enhanced Defense, +15 Defense, +1-1.5 To Life (Based on Character Level), Replenish Life +7,+5% To Maximum Lightning Resist, All Resistances +25-30, Damage Reduced By 7.
#3- 160/60 Armor- Use this if you can't reach the last FPA with your setup.