Purpose: So, yes, while this is a functional standalone plugin, it's purpose is meant to be to guide players as to how it was made and allow them to modify the foundational code to give custom functionality. Yes, this base version allows you to teleport around like a maniac with a portal gun, but it's current implementation is quite rough because it is made to ultimately be modified to specific use cases.

Requirements: You (optionally) need to either incorporate files in this resource pack into your server's resource pack, or have clients just install this themselves if you want to see the portal gun instead of a cake. https://www.dropbox.com/s/73w8564xyzaafrq/PortalGun.zip?dl=0

⟿ Actual Portal Gun: You uh... you get an actual portal gun so that's cool?
⟿ Conserved Momentum: Did you enter a portal heading upwards relative to that portal? Well guess what. You're exiting the other portal heading upwards relative to it now.
⟿ Yaw Adjustment: Although you can't actually SEE THROUGH the portals like in the game Portal, your character's yaw and pitch now function similarly to how it would in the game upon traversing portals.
⟿ Doesn't Look Absolutely Hideous: Others have definitely made this plugin before, however, they seemed to either make it functional or aesthetic. Either the portals look absolutely terrible and work, or they look good and function very questionably.

⟿ Type "portalgun" in Chat: Again, this is not meant to be standalone. It is meant to be modified by other devs and is completely open-source and just a working foundation! Typing this in chat gives you the portal gun to be able to shoot around like a mad man.

⟿ Get a Portal Gun: Type "portalgun" in chat.
⟿ Shoot Portals: Shoot once via left click and once via right click.
⟿ Walk Through: Walk through your newly created portals!
⟿ Build Momentum: Find ways to go fast as f*ck boiiiii.