Best mirror abilities to use [spoilers?]

[nickwithtea]

While I know much of them are personal preference, I've just unlocked the last of the mirror abilities and reset all my stats

I've got about 3,700 darkness points to use and was wondering if anyone has some suggestions on what is best

For example is increasing my chance of legendary/duo boons better than a boons chance to be rare? Also what's better, initial damage to undamaged foes or back stab damage. I was thinking backstab since it can be used several times per run etc

[squat_instructor]

Touchy topic as you will find lovers/haters of each mirror upgrade. For those mentioned the damage to undamaged foes perk is very useful on burst builds for clearing rooms. Legendary/Duo boost is obviously useful for builds that heavily rely on a legendary/duo like Hunting Blades, so it's rather situational.

There are use cases for most of them, it's just that some are VERY niche and situational.

[begulinggg]

Based on priority, for me, it looks like this:
1. Extra dash
2. Defiance (either death or stubborn)
3. Family Favorite or Privileged Status
4. Extra HP

The rest are complementary

[Gregor]

I like playing around the timers of Stygian Soul (3 seconds recharge on the cast)

I like starting out with 100 coins as well. HP and the Dash have been mentioned the same goes for Family Favorit and the Death Defiances which are my most used.
I prefer getting extra damage on the enemies while my cast is in them compared with them beeing slower and dealing less damage.

[Prometheus]

Ruthless dash is better than extra dash once you are good at the game.

Backstab is better for dealing with high health enemies, which are the primary threat. If they die fast enough that the full health bonus matters then they die fast enough without it.

Pickup vs timer bloodstones is build based. Not going to list every instance and caveat here.

Lodged bloodstone bonus is to preference. I prefer the damage taken.

Interest is better than start with 100 coin.

Max health. Take it.

The chance for rare/epic boons is better than the other options. Duos and Legendaries are strong but even with the bonuses they are still far from common. Much better to get reliably stronger basic boons.

Re-rolling options is stronger than re-rolling rooms. If Chaos offers you crap options this can be a lifesaver. It also refills Charon's wells. Important in the final stretch if you are using his keepsake.