When does Relentless Storm check its trigger condition, and can an opponent prevent the trigger by killing or weakening Carnivorous Snapvine after it's played but before the trigger resolves?

Ruling: When you play Carnivorous Snapvine, it enters the battlefield and both Snapvine's trigger and Relentless Storm's trigger are added to the chain simultaneously. The opponent cannot prevent Relentless Storm from triggering because the condition is checked when the unit enters, not when the trigger resolves.

Sequence:

• Snapvine is played and enters the battlefield (units always enter, nothing can prevent this)
• Both Snapvine's trigger and Relentless Storm's trigger are added to the chain
• This is the first point where opponents can react
• When Relentless Storm's trigger resolves, you may choose to exhaust the unit to channel a rune exhausted

Nuances:

• Killing Snapvine or reducing its might after it enters will not prevent Relentless Storm from triggering, since the trigger condition is not re-checked on resolution
• The "may exhaust" choice happens when the trigger resolves, not when it's added to the chain
• Opponents can react to the triggers on the chain, but cannot react to the unit being played itself