Sandstorm Crasher

The token created by the reflexive triggered ability copies exactly what was printed on the original creature and nothing else (unless that creature is copying something else or is a token; see below). 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, or so on. If it is a Vehicle, it is not crewed.

If the copied creature is a token, the token that's created copies the original characteristics of that token as stated by the effect that created the token, with the listed exceptions.

You can exert Sandstorm Crasher as you declare it as an attacking creature. You can't do so later in combat, and creatures put onto the battlefield attacking can't be exerted. Any abilities that trigger on exerting an attacking creature will resolve before blockers are declared.