This new mechanic involves item frames and boss summons. If you hadn't guessed, you can send wire signals to item frames to fight them!
When the signal is sent, it acts exactly like you trying to summon it. It does not consume the item if it cannot be spawned (mech bosses and night), it gives you a minute to prepare for the moon lord, pirates, goblins, etc.
The Lhizard power cell is consumed, and the golem spawns. To counteract the usage of an arena, the golem is charged with the electricity of the wire. It now inflicts electrified on contact!
The vodoo doll is consumed and the guide dies. The WoF spawns at the nearest edge of hell.