What spell is this...

[RigaMortus]

Not sure if this is a spell or feat or class ability, but it basically allows your next attack roll to be a critical hit. What is the name of this spell/feat/ability and in what book can I find it please?

 

[Crothian]

There's a ranger spell from Magic of Faerun that does that with ranged attack. Hunter's mercy I think it's called. There';s a feat in Mercaniaries that also does this, but you must give up an attack.

 

[Mr Fidgit]

Crothian's got it right. Magic of Faerun, pg 101

Hunter's Mercy

transmutation
Level: Rgr 1
Comp: V, S
time: 1 action
Range: Personal
Target: you
duration: see below

this transmutation makes a bow strike true, Your next attack with a bow (if made before the end of the next round) hits and automatically threatens a critical hit. if you don't hit in the round following the casting of this spell, the effect is wasted


so, you still have to roll to confirm the critical, i guess (that last line is puzzling, but there's nothing in the errata about it)

 

[Jeremy]

There is also a feat called "Power Critical" that can be used with a melee weapon to make one hit an automatic critical as well. It's in Masters of the Wild.