What is not settled yet, said plainly. None of this has been filled in by guessing.
tabla_pareja_oleada_9, eight bytes: four pairs. What is now measured is when it changes — the index comes off bits 6 and 7 of the counter at 0x55C7, so the pair alternates every 256 frames — and what each byte is: the first goes into the low half of the enemy's falling speed (0x80 or 0x00) and the second is its sprite pattern (0x7C or 0x74). Two looks with two speeds.
What is still unknown is why: what that alternation is for in wave 9 and in no other. Outside it the game always uses 0x7C / 0x80.
The table at 0x535F dispatches twenty-one object routines, and each one is identified by what it does with its 16-byte slot. What is missing is naming them for what they are on screen, and that needs playing the game and looking. For now they are OBJETO_TIPO_n with a sentence on what each one does.