How many plot twist can you play a turn? And when? Say my magneto master of magnatism attacks wolverine(6/6) and my opponet plays nasty suprise can he also play finishing move too?

You can play as many plot twists as you want so long as you have at least as many cards in your resource row as the highest threshold cost on the plot twists.

For example:

Let's say it is turn 3 and you have three PT in your resourse row. One has a threshold of 1, the next a threshold of 2, and the last a threshold of 3. In your hand you have a PT with a cost if 2 and a second with a cost of 3. You could play all 5 of these PT at the same time if you wished.

As for when, as far as I can see, you can play TP whenever you want.

Dave is 100% correct. Some PT's require you too play them in certain steps, but otherwise you can play as many as you have as long as you have the required threshold cost.