Activate only when an effect is activated that would destroy 2 or more cards you control. Negate the effect and destroy that card. Then, you can Special Summon 1 "Stardust Dragon" from your Extra Deck.
Ok just want to clarify something that I encountered during one of the tourneys.
Situation: *if i remember correctly >.<*
My field has Earth, and I normal summon Venus which then summons 3 mystic shine balls
Summon last shine ball
Chain 1: Venus summons Shine ball
Chain 2: Opponent Chains Torrential Tribute
Chain 3: I chain Starlight road
Chain 4: Opponent Chains Icarus Attack and targets 2 monsters
Chain 4: Icarus destroys 2 monsters
Chain 3: Starlight Road negates Torrential Tribute
Chain 2: Torrential Tribute is negated
Chain 1: Shine ball summoned successfully
Ok my memory was a bit blur so I just need to clarify something.
Case A (which i think is what happened)
Icarus Destroyed the last shine ball that was summoned -> starlight road did not manage to protect, hence stardust dragon could not be summoned
Case B (which i want to clarify)
If icarus destroyed other monsters which starlight road did not manage to protect, hence stardust dragon could not be summoned
Case C (what if)
Can Starlight Road actually still activate when the field conditions change? Example : from 4 monsters, the targets become 2, or even 1. In this case what happens?
I tried to translate jap wiki but it ended in utter failure lol. Thanks in advance for the clarifications!