Megaphone

Silence immunity on its own is a footnote. Being unable to attack for a few seconds only ever matters when something is already chewing on you, and by Hardmode most of that gets solved by not standing still. The real reason to hang onto this trinket is that it is one of the ten small immunity pieces that eventually fold into the Ankh Shield, which is worth an accessory slot from the moment you finish it until the credits.

Pixies are the sane target. They come in numbers on any open Hallowed surface at night, they die to anything, and you can sit in an arena and let them walk into you. The mummy sources want a converted desert and trickle far slower. Shimmer will turn one of these into a Nazar or the other way round, and since Cursed Skulls in the Dungeon hand out Nazars before Hardmode even starts, that swap is the only way to hold a Megaphone early. It does not shorten the grind, though. The combine wants one of each, so converting the one you have just moves the problem.