Spark is a new function in the game, which unlocks once you have unlocked live events. With it you can power up your AB Transformers characters for better rewards in events. It is a permanent feature and you can keep adding sparks to a character to keep powering them up. The sparks you have used to promote your bots do stay on though the tournament changes. Moreover, Spark can be found in both Steel and Gold crates, Spark Run, the Token Exchange, Daily Quests and Special Bundles.