Missile Mount: It's a flying mount. Double tap for a long dash? It has limited flight time ala the Hornet Mount.
Mecha Mount: Gives a buff to defense. Has limited flight abilities, like a longer lasting Rocket Boots. Double tap and it'll shoot out a rocket punch that does low damage but has high knockback.
Robo-Butler/Simalacrum: Requires gathering a large number of items and materials to create an NPC that just kinda walks around and gets killed during invasions, so you'd have to go through the trouble of rebuilding it. It can wear armor/vanity items, but only as vanity.
Composite Golem: Requires 50 bars each of Paladium, Orichalum and Adamantite (or their counterparts). Creates a golem that glows and follows you around. It's basically a light source pet.
Gold-lem: 200 gold ore and 50 gold coins. A pet.
Silver lining: 50 silver ore, accessory that makes you emit a soft silver light. Useful for early mining/exploration. Possibly increases your crit chance by 1% (because it's lucky/a silver lining)
Pi-Cat-so: A Picasso-ish painting of a
cat.
Itsaliveanator: A placeable item. It has like, electrical rods and stuff. But also a space in the middle where you can place items on. Items like piggy banks and grave markers/headstones. Oh, and if you hook wires and a lever to it and turn it on while there's a headstone on it, it'll consume the headstone and spawn a zombie.
Composite Alloy Man Armor Set: Pre-Hardmode version: Copper, Silver and Gold. Set bonus, allows you to fly for brief periods. <- Lead/Iron not required.
Composite Alloy Man Mk II Armor Set: Post-Hardmode version: Paladium, Orichalum, Adamantite. Set bonus, allows you to fly for longer periods.
So it's like, having a Hornet/UFO, only you can fit through doors.
Composite Alloy Monger Armor Set: Hellstone Bars, Meteorite Bars and Crimtane. Set Bonus: Do more damage (sort of like having an avenger emblem).