@rayquazaman:
The % abilities have been brought up earlier in the thread, and Tieskey argued for why they're useful. You should figure this out by doing math, so you understand your actual chances at success or failure rather than going by gut feelings. The way you're supposed to use them is for the grand scheme of things, rather than for short, specific instances.
Vampires can paralyse a unit in 6 blows. A 50% evasion unit has a 98.4% of avoiding one of those blows. They are the most effective units for dealing with them outside of units with 100% evasion or status ailment immunity. Due to their cheap deployment cost, if your rogue happens to fail too many evasions and becomes paralysed, you can consider a contingency plan beforehand. For example, you can deploy another rogue, and then go back to having another 98.4% chance of not failing in 6 blows, or—since you have more deployment points now—you can consider dropping one of your strong interceptor characters (i.e. Ricca or Karma). With a second rogue, you would have to be exceptionally unlucky for it to happen twice in the same trip.
Things you shouldn't count on is stuff like Princess Olivia's skill at 1/5 when she has to duel a monster that can one-shot her. 80% looks like you have a high chance of success, but that's the furthest thing from the truth. A 20% chance of being instantly turned into a bloody stain per blow is way too high to consider exploiting unless you're absolutely desperate.
Number of Blows (Chance of Dying):
1 (20%), 2 (36%), 3 (48%), 4 (59%), 5 (67%), 6 (73%), 7 (79%)
A LV80 Olivia can kill a 20,000HP Black Oni by herself in 22 hits, which is 726 frames (6 black oni blows). So she has a pretty low chance of surviving long enough to defeat one of these things with her skill at 1/5. This was a real scenario during Sorano's event that challenged the players to deal with two black oni, and players had to use all sorts of crazy strategies to get 3-stars. Back then, having Olivia at LV80 wasn't feasible, so most players had to use a LV40-50 Olivia (28 hits in 937 frames, which is 7 blows with no help).
Finally, a lot of these abilities stack. Gigant Armour Maribelle has only a 10% chance of nullifying damage, but against certain physical ranged opponents, Maribelle can also activate her skill so that she has a 10-50% chance of nullifying that damage. Deploy Dominion Chloe and Maribelle now has an extra 6% chance of nullifying damage. Finally, deploy the Platinum Mage Sasha, and have her activate her skill and give Maribelle 50% evasion on top of everything else. You would have to force yourself into a retarded situation like the above with Olivia where you aren't going to benefit from all of this for the vast majority of your trips to difficult god-tier maps.
Most people's issue with random chance abilities are psychological. It's the same silly thing with people being encouraged to waste their money on premium summoning when they see someone get something good, rather than doing the math and realising that they're highly liable to become suckers, and should stop while they're still ahead.
