Tuffnut: "Wait. I think I just had another idea. Whoa! Do you know how many Loki-ish thoughts are running through my mind right now?"
Astrid: "Tuffnut. This is not the time for pranks, or Loki-ing."[src]
When the Edge is attacked by Dragon Hunters and Berserkers, and Astrid and Tuffnut are the only ones left to protect it, the latter has the idea of pranking the attackers, calling it "Loki-ing".
Tuffnut: "On Loki Day?"
Ruffnut: "The day of our favorite god's birth?"
Tuffnut: "One of the greatest days of pranking ever conceived by any man, woman, child, animal, vegetable, mineral or rock?"
— Shock and Awe
It is shown in "Shock and Awe" that there is a holiday called Loki Day, which celebrates Loki's birthday by pulling pranks on others. When the prank is accomplished, the instigators shout "Loki'd!" at those who fell for their pranks.
I look around the town and I see that there's something clearly missing: the blessings of Loki![src]
During Snoggletog, everyone puts decorations around Berk, but Ruffnut feels like the blessings of Loki are missing. She then proceeds to create Loki's Maze of Cheers and challenges the player to finish it.
To appropriate an old phrase, idle "claws" are Loki's playthings.
In the expansion "Battle for the Edge", Skulder encounters a Mudraker which keeps destroying his camp. He asks the player for help, telling him/her about an old phrase: "Idle claws are Loki's playthings".
A wooden shield with Loki's head painted on it is a battle gear available for purchase from the store.