Thing-Thing Arena 3 Great Game
I play it so often, I almost quite Halo for it.
I hope to see TTA4 soon!
Also, answering the two most important questions:
To perform an execution, you must be using the lead pipe, and standing behind your enemy, then press F (or the key you set for it)
to get the Artifact 19, you must get all other medals in-game, except TRIED EM ALL and DIVINE POWERS. Or, you have to get TRIED EM ALL to obtain it, idk.