The 1 V saturation at 200 mA and minimum DC current gain of 12 at 40 mA give the base-drive designer a clear budget: at the 200 mA load point the base current needs to be at least 17 mA to guarantee saturation, and the 5 V Vce condition for the hFE measurement is a realistic switching bias.
The DPAK (TO-252) footprint with two leads plus the tab is the same as the standard SC-63 land pattern. The 20 W maximum power rating assumes the tab is soldered to a sufficient copper area on the PCB — without that thermal via stitch to the inner layers, the junction temperature will exceed the 150 °C maximum long before you reach 20 W. The 150 °C junction temperature rating is the absolute ceiling; for reliability in a 85 °C ambient environment, derate the power dissipation by the thermal resistance from junction to ambient (not provided here, but typically 80–100 °C/W for a DPAK on a minimal pad).