Eye of Cthulhu
45 and 46 are YYEESS45. At first, the Crimson, the Hallowed, and the Corruption live in relative peace. However, the Terrarians discover a new desolate wasteland who presents a great danger. Appropiately called the Desolate, a new race of Shadowed Terrarians threaten to cause havok. But maybe they're misunderstood?
46. Terrarians discover Uranium, causing an industrial boom. Then some Terrorist group called the Chaos Anarchists drop a more radioactive boom. The main problem is that radiation destroys a Terrarian's mana, and worse, prevents young children from developing a natural immunity to the taint of the Corruption. Terrarians must find a way to survive long enough to find the leader of the Chaos Anarchists, in order to use his Rod of Discord to fix this whole fiasco.
47. Terraria in the style of Command & Conquer: Red Alert series
Hallow = Allies (Magic)
Crimson = Soviets (Brutal strength)
Corruption = Yuri (Mind Control and stuff. Or Empire of the Rising Sun.)
48. RWBY, but in the Terraria universe instead.