A 2-1-2 forecheck is aggressive and can be used in many situations. In this video, NHL Hall of Famer, Denis Savard explains in-depth how to run the 2-1-2 forecheck. The first objective is a good dump. The goal is to get the puck into one of the corners. Then it is crucial for F1 and to take the proper inside out route and pressure the puck hard. The second player (F2) first has to recognize that they are the second player on the forecheck and cheat to the weak side of the ice. The third forward has to be disciplined and stay in the middle of the ice in the high slot. Both of the defense will seal the walls which make it even more important for F3 to make sure they stay in the high slot.
If the puck moves up one of the walls then the defense have the green light to pinch and try to force a turnover along the wall. If this happens then F3 has to take the position of the pinching defense. If F3 is not disciplined and creeps to low into the zone then they will not be able to cover for the pinching defense.