[MSc] A new weapon. The Scepter. (plus some extra lore on the Stave and Dungeon Wand thrown in, check comments)

The Scepter joins the Dungeon wand and Stave in the class of magic weapons. It is made out of rose quartz, wood, and Demiselite, making it available in progression just after you research Demiselite Metalworking, but it doesn't require lots of precious metal like the Pneu-Matic Substrate Cannon or The Amenbreaker.
Its main use is simple but effective healing spells, but if you're willing to look into the basic spell-crafting preliminaries for Stave usage early, you can make it hold up a defense spell instead.
Similarly, with those same preliminaries, you can make the Dungeon Wand cast a different offensive spell of your crafting.
The Stave is still superior since it can handle 2 spells at the same time, which can be upgraded to 3, and potentially overclocked to 4 with clever enough spell-crafting.

It's a magic weapon so what's it's use time, the mana cost, and is the mana cost made free by wearing Meteor armor?

MSMGCraft, while inspired by Terraria, is a separate game (according to the lore). I will answer your questions anyways.
It spends 10 arcana for the smallest healing spell, 16 arcana for the second one, and 25 arcana for the third tier. In Terraria numbers, it would have a use time of 20. (numbers subject to change)
I'll design a Mage armor set for the game later. It'll probably be crafted with Gold.

looks like a butt plug

get your head out of the gutter