Instructions
Obtain the Wave Incense from Route 47. The Wave Incense is on a lower ledge that can only be climbed with the "Rock Climb" move.
Capture a female Mantine and any male Pokemon from the Water 1 egg group. Examples of male Pokemon that can breed with a female Mantine include Clampearl, Gorebyss and Huntail. Mantine are not found in the oceans of "Pokemon SoulSilver," so you will need to trade it to your game.
Give the female Mantine the Wave Incense to hold. Select the Mantine in your party, choose the "Item" option and then the "Give" option. Scroll through your item bag and pick the Wave Incense to equip Mantine.
Drop off the Mantine and the male "Water 1" egg group Pokemon at the Day Care Center on Route 34. The Day Care is a red-roofed building found halfway down Route 34.
Visit the Day Care Center after taking a large number of steps. Talk to the woman behind the counter to see if the two Pokemon you left in their care produced an egg.
Keep the egg with you and continue on your adventure. The egg will hatch into a Mantyke after a predetermined number of steps. Riding your bike speeds up the hatching process.