We saw Jarul get stabbed in Silhouette, not in full. We were told Loki stabbed Jarul in the head.
What is that's not a lie?
If Imu actually Domi Reversi'd Harald, the guy who fought Rocks to a draw, there's no way an older Jarul, pre-New-World Loki, and some Giant Guards are taking him down without hax.
So, how did Loki kill Domi Reversi Harald?
Domi Reversi makes the user grow drastically in size; I also believe you need CoC to overcome it (and strong CoC). Here's what I think went down:
-Jarul and Loki try to fight Harald but can't do anything, he's too strong. They're the only ones who can resist, because they both have CoC
-Giants are dying left and right, and Jarul realizes Harald will destroy Elbaph
-Jarul grabs Harald, and tells Loki to stab him
-Loki stabs through Harald's stomach/chest: the sword exits straight into Jarul's head and pierces his helmet.
-Harald reverts back to normal, and tells Loki something Oda offscreens, before he dies
-Since Harald shrinks back down, the sword cuts through his upper abdomen/shoulder, leaving the sword out of Harald, and stuck in Jarul's head
-Shanks and Gyaban show up to see Loki covered in Harald's blood surrounded by dead Giants
-Jarul has memory loss of the incident from the sword hitting his head