While mrna strands are being created a sequence is sometimes miscopied. what is the best possible outcome, the worst possible outcome and the long-term effect on the cell if mrna strands were miscopied?

The best and worst possible outcome and the long-term effect on the cell if mRNA strands were miscopied is that the cell will not make functional proteins from that mRNA strand. The best and at the same time worst possible outcome is that the cell will not make functional proteins from the mRNA strand.