Portal Gun

The Moon Lord always leaves one behind, so it is not a roll you have to chase. In Expert the treasure bag checks your inventory and skips the gun if you are already carrying one, which means you cannot stockpile spares by farming him. The other thing to do on the way home is talk to the Cyborg while it is on you: he only offers the Portal Gun Station once he can see you own the gun.

Left click places one end, right click places the other, and anything that walks into one comes out of the other still moving at the speed it arrived with. Only you and the town NPCs make the trip. Enemies, critters, items, projectiles and liquids all stay where they are, so it is a travel tool and never a weapon or a pump. Grappling hooks release the moment you go through, and a mount or a minecart cannot pass at all, so you dismount first or you do not go.

Just holding it changes how the character handles. You fall several times faster than normal and you keep horizontal momentum in midair instead of bleeding it off, whether or not a portal exists anywhere in the world. Swapping to it mid jump is enough to change where that jump lands. The same heavier fall carries over for a moment after a portal was the last thing to touch you. None of it applies while you are riding something, so a mount cancels the whole effect.

Because speed survives the trip, a long drop into a floor portal comes out of a wall portal as pure horizontal speed. That alone crosses a world faster than wings. The extreme version stacks two portals inside a water chute and enters the chute from as far away as the placement allows, at which point you are moving quickly enough that steering is the entire difficulty. Wings that hover well, or anything that holds your speed steady, turn it from a party trick into actual transport. You will overshoot the first several attempts.

A portal needs a short run of blocks in a line to sit on, and it will take that surface at any angle, including diagonals. Two portals cannot overlap, so placing a new one on top of an old one simply replaces it. Break or actuate any tile of the surface and the portal goes with it, which is what makes blocks conjured by an Ice Rod a usable but temporary anchor. Liquids are fine to shoot into. Anti-Portal Blocks refuse them outright, and the Creative Shock the Old One's Army inflicts blocks placement for the length of that event.

Portals also do not follow you around. Wander far enough away, die, or leave the world and they are gone. The bolt itself travels a long way but takes a couple of seconds to get there, so a shot fired across a large cavern lands well after you expected it to.

• Two portals both facing upward will bounce you between them forever, which is funny once and a nuisance in a fight.
• Going through resets fall damage but does nothing for your wing timer, so it cannot be used to stay airborne indefinitely.
• Whatever you are standing on affects you before the portal does. One placed on damaging blocks hurts you on the way in, and one on pink slime bounces you off the surface instead of letting you enter.
• If both ends are on screen at once the camera slides across rather than cutting, which reads as lag the first time you see it.
• In multiplayer every player gets their own portal colors so nobody walks into somebody else's shortcut by mistake.

The whole thing is lifted from the 2007 puzzle game of the same name, down to the orange and blue and the line of flavor text, which is a quote from that game's antagonist explaining that momentum is conserved. Even the source of the gun is a joke: the sequel ends with the player firing a portal onto the surface of the moon, and here it comes off the corpse of the Moon Lord.