What cards can be played to trigger 'when you play a spell' effects without affecting the board state?

Ruling: You can play Bullet Time to deal 0 damage (even with units on the battlefield), and you can play Icathian Rain/Falling Star with no units on the board. These will trigger 'when you play a spell' effects.

Nuances:

• Bullet Time can deal 0 damage even if the battlefield isn't empty
• If you control a unit and play Falling Star/Icathian Rain, the triggered abilities they create must target legal targets if any exist, and your own units are legal targets
• For Ravenbloom Student and similar effects, only the initial spell (Rain/Falling Star) counts as +1 spell played; the triggered reflex abilities do not count as additional spells played