After conquering R'yleh and the Frozen Kingdom young Howard Lovecraft must now travel to the Undersea Kingdom in order to free his captured family, protect three mysterious magical books, and prevent the impending wrath of Cthulhu.
| Actor | Role |
|---|---|
 Kiefer O'ReillyHoward Lovecraft / Davik (voice) | Howard Lovecraft / Davik (voice) |
| MMichelle MyersMichelle Lovecraft (voice) | Michelle Lovecraft (voice) |
| SSummer O'ReillyGotha (voice) | Gotha (voice) |
| PPhoenix O'ReillyTwi'i (voice) | Twi'i (voice) |
| HHarmony O'ReillyInnes (voice) | Innes (voice) |
 Scott McNeilGovlins / Ice Govlin 'Barry' / Dagon (voice) | Govlins / Ice Govlin 'Barry' / Dagon (voice) |
| SSean Patrick O'ReillySpot (voice) | Spot (voice) |
 Jeffrey CombsKing Abdul (voice) | King Abdul (voice) |
 Ron PerlmanShoggoth (voice) | Shoggoth (voice) |
 Doug BradleyThe Envoy / Nyarlathotep (voice) | The Envoy / Nyarlathotep (voice) |
 Mark HamillDr. Henry Armitage (voice) | Dr. Henry Armitage (voice) |
 Tyler NicolWinfield Lovecraft (voice) | Winfield Lovecraft (voice) |
 Christopher PlummerDr. West (voice) | Dr. West (voice) |