No horse can match the impact of Into Mischief, a 21-year-old stallion with three Derby-winning offspring and three more competing Saturday. LEXINGTON, Ky. — At 2:08 p.m. last Wednesday, the heavy wooden door to one of the two breeding sheds at Spendthrift Farm rolls open. In walks a bay-colored, boxy horse with a prominent white blaze on his face and white markings on two of his feet. In... [11676 chars]