NightFall Proc %

Numbers for NightFall rank 1:

Nightfall 1 chance to proc 2% per tick of drain life (5 ticks,5secs):
1-(.98^5)=10% chance to proc over course of spell

Nightfall 1 chance to proc 2% per tick of corruption(9 ticks,27 secs):
1-(.98^9)=17% chance to proc over course of spell

Casting additional corruptions on different targets would be a sum for chance to proc, so 17% per corruption casted going the full duration

Casting simultaneously with 4 drainlifes over the course of corruption:
17 + (10*4)=57% chance to proc

Numbers for NightFall rank 2

Nightfall 2 chance to proc 3% per tick of drain life (5 ticks,5secs):
1-(.97^5)=14% chance to proc over course of spell

Nightfall 2 chance to proc 3% per tick of corruption(9 ticks,27 secs):
1-(.97^9)=24% chance to proc over course of spell

Casting additional corruptions on different targets would be a sum for chance to proc, so 24% per corruption casted going the full duration

Casting simultaneously with 4 drainlifes over the course of corruption:
24+(17*4) = 92% chance to proc