There are two differences between the prototype of this game and the final build:

  1. A few instructions change between the two builds: the prototype sometimes uses the I register to hold a temporary, while the final build uses a RAM location instead ($c200). Since the memory access instructions used are 3 bytes long while the instructions to access the I register are only 2, these few instruction differences cause a large number of addresses to differ, mostly by 2 or 3 bytes.
  2. The prototype does not contain a product code in its ROM header.

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