Does Riftbound have target loss where a spell fizzles if the targeted unit moves to a different location before the spell resolves?

Ruling: No, Riftbound does not have target loss. Spells resolve to the best of their abilities - if a target is no longer valid at resolution, that part of the effect is ignored but other parts of the spell still resolve.

Sequence:

• Targets must be declared when casting a spell or ability (with exceptions for reflexive triggers)
• If the target moves or becomes invalid before resolution, the targeting instruction is ignored
• Other effects on the card still resolve normally
• Targets will "chase" as long as they remain legal targets (e.g., moving from one battlefield to another battlefield)

Nuances:

• Reflexive triggers (like Falling Star and Icathian Rain with "do this X times" text) don't require targeting on cast - they create instances that target upon resolution
• These reflexive triggers can still be responded to after targeting but before they resolve
• Targets chase as long as the permanent exists in a legal zone and meets targeting restrictions