For abilities with 'may' in their text (like Startipped Peak), is the choice made when the ability is activated or when it resolves?

Ruling: May choices are made on resolution. The trigger always goes onto the chain, and as it resolves, the controller may choose to do the effect.

Sequence:

• The trigger goes onto the chain (this always happens)
• The trigger resolves
• On resolution, the controller chooses whether to use the may effect

Nuances:

• This applies to all "when [trigger], you may do" effects - they always go onto the chain and then optionally have an effect
• You cannot skip putting the trigger on the chain to avoid starting a chain