This is probably more a general magic issue than a Ranger issue, but it is unfortunate that a mana-capped Grizzly Claw is unable to function at all against these undead.
The mana you were holding contributes to the spell.
You manage to channel most of your energy into the spell. The rest is wasted.
You roar and draw your arms back. A dark, transparent blue glow ripples down your arms, crackling with the muted growl of a bear as it shapes itself into two large claws.
You lash out with both arms, sending a concussive wave of blue force outwards all around you!
The spell pattern collapses at the last moment due to its undead state.
The spell pattern collapses at the last moment due to its undead state.
The spell pattern collapses at the last moment due to its undead state.
The spell pattern collapses at the last moment due to its undead state.
The bluish energy forming the claws disperses into the air after the attack.