A 2D game called Deer Hunter has projectiles like this:
Are the projectiles 2D or 3D models? How could I implement something similar?
I've made projectiles like this in a game and they are most likely 2D for all purposes besides selecting the correct sprite. Then a third Height variable is maintained and some simplified physics is applied. This variable might even be "time in air". So they are likely represented in 2D (x,y) and animated using a third tertiary variable
3D models for something that uses minimalist art is completely overkill. The arrows' effects are most likely produced by 2D art and some math.
First, the arrows are given a rotation based on the angle that the player makes with the mouse, upon release of the left mouse button.
Then, based upon how long the mouse button was held, the arrows are given a flight time.
Finally, upon reaching the end of their flight time, the arrows will be animated to angle toward the ground and have their height reduced by a small amount.
Once again, this is, or at least should be, done with 2D art that is rotated based upon the angle being shot at.
By speculation - this is what it looks like to me.
I'd say that this game (and the darts) should be and probably is made in 2D because:
Anyway, this is all mostly speculation - but hey, you asked us to look at a gif and tell you how we think it was done, so I guess speculation is okay. :P
Although, despite this being speculation, I think it's actually how the game should be done if it was not already done this way. Although there's plenty of other answers here and I'd say any of them would probably work well. Eh, I hope this answer helps you some way. :)