Skills
The below builds require at least 101 health. Generally, equipment wise, it is good to have physical weapon + energy aux + energy aux OR [energy weapon + physical gun + physical aux].
As you have learned from the passage above, mercenaries require maximum hybrid. There is no choice. So far the only types of successful mercenaries are strength, support and sometimes tech. Strength and tech is generally 1v1 and support is generally 2v2. Strength builds generally tend to distribute points as max hybrid, max FC, 1 berserker, some in heal and some in intimidate. Strength builds need OK strength (unless you're not using FC, then you need relatively high strength), 40-50 without stat modifiers. You also need good DEX because you do not want to block a ton. Tech, and your stat mod need to give you around 20-24 resistance and support should be decent. Tech builds generally have a max SS with high tech. You can choose to play a bunker along with it but it hamper your play because you need so much manna. With this high tech and hybrid you should have a very nice defence. Have 101 hp and 59 manna (or more if you are using bunker, but not recommended). Use weapon, gun and aux to get their HP down and then use SS to give them a ton of damage and take their rage. If you have bunker, rage it next. For the skill tree, if you are not using bunker, have max SS, max hybrid and 7 heal. The rest of the points can be anywhere. The level-7-heal is for 2 heals instead of a max SS.