Can an opponent play reactions when you play a creature or permanent without an on-play ability, and can you react to spells being played?

Ruling: Players cannot react to a permanent (like a creature) being played unless that permanent triggers an ability. Players can always react to a spell being played, which goes on the chain and only resolves when all relevant players consecutively pass.

Nuances:

• Accelerate is an additional cost, not a triggered ability, so paying accelerate does not pass priority or open a window for opponent responses
• Priority is never passed when playing a permanent without triggered abilities