The old route, about 4 seconds slower than the new route. It requires 10 star coins.

1-1 - Get the 1st star coin 1-2 1-3 - Get the 1st star coin 1-Tower - Get the 1st and 3rd star coins 1-4 - Get the 1st star coin 1-A 1-Castle - Get the 1st star coin 2-1 - Get the 3rd star coin 2-2 - Get the 1st star coin 2-3 2-Tower 2-Ghost House (Secret Exit) 2-B 2-Castle - Get the 1st and 2nd star coins 3-1 3-A 3-Tower 3-4 3-Ghost House (Secret Exit) 3-Castle 4-1 4-Ghost House (Secret Exit) 4-B 4-Castle 5-1 (Secret Exit) 5-Ghost House (Secret Exit) 5-A (Secret Exit) 5-Castle 6-1 6-Ghost House (Secret Exit) 6-A 6-Tower 6-4 6-5 6-Castle

Here are some star coin substitutes that won't waste much time: 1-1 - The 2nd star coin 1-2 - The 1st star coin 1-3 - The 3rd star coin 1-A - The 2nd star coin 2-B - The 3rd star coin 2-Ghost House - the 1st and 2nd star coins 3-1 - The 1st and 3rd star coins