Reaver Titan

• WOTC Official Reminder Textofficial rules
  Protection — This permanent can't be damaged, enchanted, equipped, blocked, or targeted by [quality].
• WOTC Official Reminder Textofficial rules
  Crew — Tap any number of creatures you control with total power N or greater: This Vehicle becomes an artifact creature until end of turn.

• WWizards of the Coast2022-10-07
  Official Ruling
  The protection ability means the following: - Reaver Titan can't be blocked by creatures with mana value 3 or less. - Reaver Titan can't be enchanted by Auras with mana value 3 or less. It also can't be equipped by Equipment with mana value 3 or less. - Reaver Titan can't be targeted by spells with mana value 3 or less. It also can't be targeted by abilities from sources with mana value 3 or less. - All damage that would be dealt to Reaver Titan by sources with mana value 3 or less is prevented.
• WWizards of the Coast2022-10-07
  Official Ruling
  While a spell with X in its cost is on the stack, its mana value takes the chosen value of X into account. Reaver Titan can be chosen as a target for a Light Up the Night (which has mana cost ) if X is 3 or greater, for example, but it can't be chosen as a target for a Light Up the Night if X is 2, 1, or 0.

Rulings via Scryfall