You'll need:
A size "G" crochet hook
Some yarn in a color of your choice for the body (A)
A little bit of white/beige yarn for the horn (B)
Fiberfill
12 mm safety eyes
Yarn needle
Body:
Rnd 1: With A, ch 5, join to form ring, place marker. (5)
Rnd 2: [inc] around. (10)
Rnd 3: [inc, sc] around. (15)
Rnd 4: [inc, 2 sc] around. (20)
Rnd 5: [inc, 3 sc] around. (25)
Rnd 6-9: [sc] around. (25)
*Attach safety eyes to front for the face, stuff as you work the rest of the body*
Rnd 10: [dec, 2 sc] 4 times, sc to end. (21)
Rnd 11: [sc] around. (21)
Rnd 12: [dec, sc] 4 times, sc to end. (17)
Rnd 13-16: [sc] around. (17)
Rnd 17: [dec, sc] 5 times. (12)
Rnd 18: press the back flat, and sc along to close it up.
To make the fins:
Ch 1, turn, sc in first 2 chains from hook. Turn, sc in last chain. Ch 1, turn, sc along back. The first back fin is done! Now, turn and sc in next 2 chains from the hook. Slip stitch in the next chain and fasten off! Weave in ends.
To make the horn:
Rnd 1: With B, ch 4, join to form ring, place marker. (4)
Rnd 2: [sc] around. (4)
Rnd 3: [inc] around. (8)
Rnd 4-5: [sc] around. (8)
Fasten off, leaving a long tail for sewing.
Attach the horn to the center of the narwhal's forehead. And there you go! :D