Kris Letang of the Pittsburgh Penguins. Charles LeClaire-Imagn Images We have our first elimination day of the Stanley Cup Playoffs on Saturday, and those interested in getting in on the DFS action at for this triple-header can line up an exclusive promotion at Underdog : Play $5, and get $50 in fantasy bonus entries . Saturday’s slate kicks off with a matinee between the Carolina Hurricanes and Ottawa Senators, followed by Game 4 between the Stars and Wild in Minneapolis. The Penguins and Flyers close the show in primetime. Underdog promo code NYPOST for the Stanley Cup Playoffs With the  Underdog promo code NYPOST , first time fantasy users on the platform are granted a worthwhile welcome offer at sign-up:  Play $5, get $50 in fantasy bonus entries . Fantasy players can use those bonus entries to make plays on Boston vs. St. Louis, NHL games or the Masters. DFS is among the many ways new users can put their fandom to use and get something back if they’re right.…