In Flame Chompers' triggered ability 'When you discard me, you may pay {Red} to play me', is paying {Red} a cost or part of the effect? Can you activate the ability and choose not to pay on resolution?

Ruling: Paying the fury power is part of the effect, not a cost. The "may" applies to the resolution choice - the ability goes on the chain when discarded regardless, and you choose whether to pay during resolution.

Sequence:

• When Flame Chompers is discarded, the triggered ability automatically goes on the chain
• When the ability resolves, you may choose to pay {Red}
• If you choose to pay and have the resources, Flame Chompers is played
• If you choose not to pay, nothing else happens

Nuances:

• The word "to" denotes a requirement - you cannot summon Chompers without paying the fury power, even though paying is part of the effect
• If you have no fury runes on resolution, you cannot summon Chompers because "to" creates a dependency
• When multiple abilities trigger during resolution of another ability, nothing can enter the chain while something is resolving, but once resolution completes, all triggered abilities populate the chain simultaneously
• Turn player's abilities go on chain first (resolving last), then next player in turn order