So I've been farming the Spirit Veil.

[Kitonic]

With my friend, and we noticed that when we killed the mobs at the same time we would get the same spawn(priest/mite/or skull) so we ended up looking into spawn patterns and this seemed pretty consistent. 

We used Liveclock.net to see seconds in time and got this spawn pattern within a few hours of watching it.

0 Corpse Mite Queen

1 Fetid Priest

2 Stratus Skull Captain

3 Corpse Mite Queen

4 Fetid Priest

5 Corpse Mite Queen - sometimes I also get Stratus Skull Captain

6 Fetid Priest

7 Stratus Skull Captain

8 Corpse Mite Queen

9 Stratus Skull Captain

0 Corpse Mite Queen

This goes from a fresh minute(00) and resets every 10 seconds- 10 being the fresh 00.

Now I honestly had LESS luck getting a priest with trying to time it because it takes my class too long to aoe them down but man I tried ; - ;

 

[Onbekend]

Nah, there's no pattern. There's been times I've had 10 Queens/Captains in a row, and also times where I've had 3 priests in a row.