Ladder #252 is five finishes in a row: 12, 43, 65, 98 and 103. You get one turn of three darts for each, and every finish has to end on a double or the bull.
12 is a straight double: D6. If the dart lands in the single by mistake you are left on 6, which still has a double finish with the darts you have left. 43 is a two-dart finish: 3 D20.
65 is a two-dart finish: T19 D4. 98 is a two-dart finish: T20 D19. 103 needs all three darts: T17 12 D20. If the first dart misses its treble, the board will show the new route straight away.
At best the five finishes need 10 darts out of 15. Your result counts the finishes you make first and the darts you used second. These are friendly numbers. Aim at the inside half of the double on the first dart — a miss on that side lands in the single and keeps the finish alive.