Can the chain be added to after it begins resolving?

The ability to add to a chain during its resolution is critical for understanding how interactions function in certain gameplay scenarios. In this context, when a chain begins resolving, it can indeed be altered, but it is specifically limited to the use of Reactions. Reactions are a type of effect that can trigger in response to the events occurring in the chain, allowing players to interact with the resolution in real-time.

When a chain initiates, players have the opportunity to play Reactions based on the events that are happening, which can modify the outcome or add additional effects to the chain. This understanding is essential for strategic planning, as it allows players to maximize the impact of their cards and influence the course of play even after the chain has begun to resolve.

The other options do not hold true in this context. A statement that the chain cannot be changed once it starts is overly restrictive and does not account for the strategic interactions provided by Reactions. Suggesting that only the active player can add to the chain also misrepresents how Reactions function, as any player can typically respond with their own Reactions. Lastly, asserting that changes can only occur during a Showdown confines the interaction to a specific phase, whereas Reactions can be utilized more broadly during