That's the SPNKr, Halo 5's iconic double barrelled rocket launcher in all its glory, remade with LEGO bricks by Nick Brick. Looks amazing! It's double barrelled, and you can remove the launch tubes and reload the weapon just like in the game.
Even if it only shoots imaginary rockets, made with After Effects, handling a fragile item like this requires attention. One tiny slip and the whole thing could break apart.
You can see how huge it is in the clip below:
[via Brothers Brick]