Part of the Secondary Entrance data; each byte corresponds to an entrance. The lowest 3 bits are the Mario action. The next bit is the high bit of the secondary entrance's level number. The highest bit is set when the destination level should be slippery.
Note that, as of LM v2.50, this table may be dynamically moved to accomodate the size of the new secondary exits. It can be found at read3($05DC81).