Endless Mode allows the player to grind for green shards more effectively than through Challenges. Upon collecting 5 million Gold, the player will be prompted to "Explode" for a a bonus to green shard gain. Clicking "Explode" will stop all researches and the player will have 60 seconds to collect as much gold as possible. The gold gained during this time impacts the amount of Green Shards awarded at the end.
Formula for Green Shard gain in Endless: Still needed.
Two upgrades that directly help green shard gain from Endless mode are Collector and Detonator.