It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on
While Welder is never swapping Wurmcoils and Battlespheres in and out of play in affinity it still does far far too much for a one mana card
The [c]Niv-Mizzet, Parun deck[/c] I mentioned earlier wouldnt be that great if it only worked whenever you drew [c]Curiosity[/c]
We can run Danitha, Benalias Hope lines, sneaking in Ardenn, Intrepid Archaeologist (a Kor Scout)
They are slow and vulnerable but they make up for this by also performing other roles, things to hold equipment, use in some sacrificial capacity and so forth
With the right combination of cards, it's not impossible to chai n enough extra turns to defeat the entire table of opponents once the extra turns start going off .