Complex sentence: Many enemies and objects drop halos, which resemble the rings from Sega's "Sonic the Hedgehog" games, when destroyed; the player can collect the halos to buy items, techniques and weapon upgrades.
Split into simpler sentences: Many enemies and objects drop halos when destroyed, which resemble the rings from Sega's "Sonic the Hedgehog" series. The player can collect the halos to buy items, techniques and weapon upgrades.