The introduction of Cronus Astaroth on 2014-10-20 heralded a new generation of monster hunting targets. This 5th gen was characterized by the "stance" mechanic. Each 5th+ gen monster has a stance rating. Cronus Astaroth's stance rating, for example, is 30. To qualify for legendary loot, damage on these monsters must be done with a general whose stance level at least equals the monster's. At simplest, the general's level is their stance level too. Alliancing additional generals of the same stance TYPE adds their level to th primary general's for stance level determination. Ergo, if you had aggressive-stance Dolomar at level 25 with no other generals allianced, you would not get Contribution Points to qualify for legendary loot on Cronus Astaroth. If you added aggressive-stance Barbarus at level 5 to Dolomar's alliance, though, you'd squeak by on their combined level 30 aggressive stance.

In addition to the per-location health bars and party health bars, Stance monsters (C.Astaroth, Ouroboros, Vargulis, Samael, Chromus and Phantoms) have a green "critical" meter and orange "damage" meter. Each meter starts empty at Lvl 0 and can be filled to level up by spending 250 stam on attacks with the a general of the correct stance (defensive generals for the green crit bonus meter, aggressive for the orange damage bonus meter. And finally, there is a blue "decay" meter that can be leveled up with hits from a "balanced" general. If I understand correctly, hits with balanced generals do NOT count toward contribution points.

By filling the damage and critical stance bonus meters, increasing levels of enhanced damage are unlocked.
250 stam is needed to unlock Lvl 1 in each bar (10% damage boost or 2% crit chance boost).
Another 500 stam is needed to unlock Lvl 2. (20% / 4%)
Another 1000 stam is needed to unlock Lvl 3. (30% / 6%)
Another 3000 stam is needed to unlock the "max" (Lvl 4) (50% / 8%).
If BOTH bars are maxed, "ultimate mode" is unlocked for 2 minutes, giving +100% damage and +10% crit chance.

∴ Total stam to unlock ultimate mode is 2 * (250+500+1000+3000) = 9500
Needless to say, that's a lot of stam. By the time I unlocked Ultimate Mode solo by spamming full-stam potions, I would have exceeded the legendary damage threshold, so there's some strategy involved in the math of how to share the stam and energy expenses of filling the meters so that all participants can meet their damage target goals efficiently. Two minutes in Ultimate Mode is not a lot of time; you'd probably want to limit the number of participants to around 4-6 to give everyone a turn without a lot of stumbling over each other. For every 100 stam I spend, I get around 1.5M damage (ignoring crits). Dividing the meter-filling phase among 5 players, if I spend 2000 stam I'm going to do AT LEAST 30M damage, and then in ultimate mode I'm going to do 3M per 100-stam hit but probably more like 6M on average because better-than-coin-toss odds of crits. You only need to do 102M for max legendary drop rate, so figure another 1200 stam. That is, I would reach my target with about 3200 stam: 2000 during the meter-filling phase and 1200 in Ultimate Mode.

Due to the XP cost of leveling generals past 50 or so, it's often attractive to alliance, say, aggressive Jera primary, with Dolomar secondary and Barbarus tertiary, or a defensive go-to like Katherine primary. Maalvus is a balanced general - handy for optimizing stam use but will NOT build Contribution Points. Annika is also balanced stance, awesome for reaching crunchy opponents in PvP but leveling her on monsters will not build CP. So you really want Dolomar (aggressive) at the ready.

There are no defensive generals with attractive monster hunting special abilities. In a defensive stance alliance hitting for XP, like Katherine-Dolomar-Maalvus, where the primary has no crit% but the secondary and tertiary both do, only the general with the higher crit% bonus will apply, so it should be Dolomar (or Kang if you have him), and leave Maalvus at home in favor of Barbarus's bonus monster damage special ability. (Kaiser has the same special ability and level progression as Slayer, so if you already had crystals and levels in Kaiser then sub him for Slayer in this discussion.)

This leads to the question... percentage point for percentage point, is it more advantageous to crank up crit chance or damage bonus? I think the base crit hit chance is 6%, but more important to know is that the average crit hit does 2.5x damage (equal chances of double or triple damage). It's a linear function where you get 2.0x damage with a 100% damage-bonus general, whereas you get 2.5x damage with a +100% crit chance general. Caveat the first is, your crit chance caps at 100%, but +X% monster damage would presumably just keep on scaling past 100%... if there were any other generals or equipment besides Barbarus and Caine with that ability.

The second caveat is, secondary and tertiary generals in a crit% alliance will have their +crit% halved or 1/3, respectively. If your Barbarus is L24, then he gives +5.2% monster damage, so you'd need a +crit% general that gives +10.4% crit in the tertiary slot to get as much long-run bonus damage as Barbarus.

In my case, I unlocked Maalvus's max level to 54 and Barbarus's to 29 before colored crystals became too precious to continue. So, even though Maalvus's +crit% lags behind Slayer's at level parity, it will not be attractive to unlock Slayer's max level to overtake Maalvus anytime soon. So my optimal pure +crit% alliance is Dolomar-Maalvus-Slayer. At max L24, Slayer's +crit% is 7.35%, vs. Barbarus's L29 6.3% monster damage bonus. So for me right now there's no point in investing further in Slayer. Based on generals I actually have, at the levels I have them, my overall optimal monster-bashing allance is Dolomar-Maalvus-Barbarus.

With all that in mind, I unlocked max levels as much as possible without spending colored crystals, and bought FP equipment for Dolomar, Maalvus and Barbarus for the 10% equip bonuses. Leveling Barbarus as primary in an alliance means only 1 secondary or tertiary general's +crit% will apply, and I didn't have FP general Caine yet, so I hired him too, for secondary with Dolomar tertiary. Barbarus and Caine's abilities do NOT appear to obey the alliance stacking pattern though.