Does a spell or ability fizzle if its target moves from one battlefield to another battlefield?

Ruling: Target requirements are checked again at resolution. If a spell targets "a unit at a battlefield" without specifying which battlefield, the target remains valid even if it moves to a different battlefield, and the effect will resolve normally.

Nuances:

• If the target moves to base or becomes otherwise invalid (not at any battlefield), the target becomes invalid and the instruction will not execute
• The effect still technically resolves even with invalid targets, but the instruction doesn't execute (this matters for cards that care about resolution like Darius Trifarian or Ravenbloom Student)
• Cards with location restrictions like "Here" (such as cards played from Hidden) require the target to be at the same specific battlefield upon resolution, or the target becomes invalid