hello! this link has some information about revelation skills. they can be learned in reliquary of the giants, from npc: monk of chaos. as for what skills to get, for tanks you can choose between those: unbind disparition undying will endurance earth tremor (it was broken, not sure if they fixed it) but in the end, it your choice. you can always change it later, if you want try another skill.
yes, at the cost of 100kk if i'm not mistaken, so choose carefully. i'd suggest disparation, prevision or unbind.
in most case, disparition/unbind is a good (the best ?) mix, except if your class has already built-in cleanse (tanks, healers), unbind won't probably be a good idea (probably take undying will in this case).
from my experience undying will its worst of those for tank healer because you cant get healed while effect, for others might be ok but for tank dont suit well in my opinion.
undying will is great. tank has huge hp pool which means the trigger for undying will is 100% certain, unlike squishy classes who can die and skip it easily. if u get on sticky situation like inside enemy lines and u know u cant get out, undying will means 100% certainty u will survive and be able to return to ur pt. most important on sieges + medusa potion.
