Question about timing of copy cards like Expansion // Explosion. I want to copy my Lightning Strike. What's the timing? Do I cast Lightning Strike and then immediately cast Expansion // Explosion? Do I cast them at the same time? Do I wait for my opponent to do something about Lightning Strike as I cast it? What if my opponent doesn't even give me time after casting Lightning Strike to copy it and he counters it? Just need clarification. Thanks!
You can cast Expansion right after you cast Lightning Strike (C.R. 601.2i, 116.1a, 708.3). However, you have to do so without knowing whether an opponent or any other player will cast an instant spell (including, say, Cancel) or activate an ability in response to Lightning Strike or Expansion (C.R. 116.1a-b, 116.7). That's because if you pass right after casting Lightning Strike, then every other player can decide to pass as well, resulting in Lightning Strike resolving and thus leaving the stack (C.R. 116.4, 116.3d; C.R. 608.2, especially 608.2k). See also this thread and this thread.
Even if they counter the Lightning Strike though, the copy from Expansion // Explosion is still on the stack as a pseudo Strike right? It will resolve separately and they can counter the copy if they want as well?
It depends. If they let the Expansion resolve, then the copy will not be affected. However, most opponents are going to counter the Lightning Strike *before* Expansion resolves. If they do, then the target for Expansion is gone and will not resolve; you will get no copy in that case.
Even if they counter the Lightning Strike though, the copy from Expansion // Explosion is still on the stack as a pseudo Strike right? It will resolve separately and they can counter the copy if they want as well?
Expansion or the original Lightning Strike can be countered before the former resolves and copies the latter. In either case, no copy of Lightning Strike will be made (and if Lightning Strike is countered, this is especially because Expansion will then have its only target illegal and fail to resolve [C.R. 601.2b]) (C.R. 701.5a). However, after Expansion copies Lightning Strike, both the original and its copy will exist as separate spells (under C.R. 706.10, a copy of a spell is itself a spell).
You can cast Expansion right after you cast Lightning Strike (C.R. 601.2i, 116.1a, 708.3). However, you have to do so without knowing whether an opponent or any other player will cast an instant spell (including, say, Cancel) or activate an ability in response to Lightning Strike or Expansion (C.R. 116.1a-b, 116.7). That's because if you pass right after casting Lightning Strike, then every other player can decide to pass as well, resulting in Lightning Strike resolving and thus leaving the stack (C.R. 116.4, 116.3d; C.R. 608.2, especially 608.2k). See also this thread and this thread.