I admire your commitment to this discussion :)

In the Three Body Trilogy, the hyper-advanced aliens use projectiles accelerated to very near the speed of light. The premise is that there's enough energy in these that their impact is an extinction-level event for the planet they hit.

There's a fun thread on Quora[1] about so-called "relativistic kinetic kill vehicles", with the top comment making the good point that a small projectile moving very fast might just punch a clean hole in the planet and keep going, thus not transferring most of its energy.

[1] https://www.quora.com/What-are-Relativistic-Kinetic-Kill-Veh...