Can you cast repulse without a spell target, just with a creature target? Just to get a ''when you play a spell effect''?

The ruling still holds (a spell with unmet target requirements can't be played), but it cites 358.1 as checking that all targets are legal, and the new text says it checks that the card made appropriate choices (targets legal, requirements met per rule 355), so the citation and reasoning need rewording.

**No.** Repulse requires *both* targets — a friendly unit at a battlefield **and** an enemy spell or ability on the chain that chooses that unit and no other friendly unit. The counter instruction is mandatory, not optional ("Counter..." with no "up to" or "may"). Without a qualifying enemy spell/ability on the chain, Repulse fails the check at finalization that the card made appropriate choices, since its targets aren't legal (Rule 358.1), and can't be played at all — even just to trigger "when you play a spell" effects. This matches the ruling for Riposte ("Choose a friendly unit and a spell"): every choice in the list is a mandatory target, and all must be legal before the spell can go on the chain.