QUESTION ABOUT MERCS

That is a complex answer :

the gear you put on them normally only benefits themselves. P.e. added strength, faster hit recovery, + life, better resists, increased attack speed, +skills, etc only influences their own performances (although you will benefit from it when your merc is fighting by your side and doing a better job).

The big exception are auras : you will directly benefit from any aura your merc has and gives to your party (that includes yourself)

It doesn't matter if that aura is inherent (built into the merc p.e. prayer aura or might aura) or if it comes from specific gear that grants him and you that aura.

If you give your merc the Insight runeword, it is pretty obvious its aura immediately influences your own mana regen. If you give Insight to a prayer merc and plant a Cure helmet on his head the different auras (3) will strenghten eachother and you will benefit enormously from the gear he is wearing (faster mana and life regen and much quicker recovery from curses)

The same goes for fanatiscism that comes from p.e. Hustle equipment. It will affect him, you and all your minions. Put a Bramble armour on him and both aura effects will stack and affect your whole party.

Auras from gear he wears that weaken or affect the enemies (p.e. if you equip him with Infinity) also benefits you in the same way. You don't get stronger but everything you want to kill gets weaker.

By the way : the same works for him. He does not directly benefit from it when you put on better gear with certain added perks, but he will benefit from the auras you radiate yourself.

There are 2 notable exceptions to this rule : he does not benefit from the Sunder charm you have equipped, but on the other hand, the Magic Find you have on your gear gets added to his (not the other way around). That is why sometimes players with a merc that has good MF on his gear will try to get the merc to get the killshot. Your MF is added to his, so his MF will be higher than your own.