Knife and Nickel's relations have been a sort of "mean friendship", as the two aren't severe enemies, but not great friends either.
Episodes Suggesting A Friendship
In One-Shot Wonder, Nickel runs over to Knife right after he escapes the LOL, Nickel explains how he was trapped in there after not joining Battle For Dream Island, but Nonexisty helped him escape from the outside. This seems to make little sense to Knife. He moves on to trying to cheer Nickel up now that he is back with some s'mores. Nickel is excited, but doesn't remember how to make s'mores. Knife states that it is simple, and demonstrates how to do so.
In War De Guacamole, Knife asks Nickel and OJ if they want to see the wonders of static electricity, to which Nickel responds "Yeah!" enthusiastically. Knife then walks over and shocks Marshmallow. He laughed at Marshmallow's misery, but was impressed when she launched him by hitting a button on a remote that caused the platform underneath Knife to launch him into a gorge.
In The Penultimate Poll, Nickel warns Knife to calm down, and comments on how he's been acting weird lately in a reprimanding tone.In A Kick in the Right Direction, Nickel was willing to offer Knife tips on how to be sarcastic, which Knife does not decline.
Episodes Suggesting A Conflict.
In A Lemony Lesson, Lightbulb suggests to Nickel that they should pick Knife since he's strong. Nickel replies "whatever", and Knife says that since they chose him he didn't have to beat them up. Nickel sarcastically commented that this was a relief since he was so terrified. Knife then kicks him. Later, after Team Epic lost the lemon challenge, Knife is amazed that they lost to Taco, but Nickel states that at least the rest of the team did something, and he and Paper had just sat there and watched Desperate Housewives, a "terrible" show.In The Arena of Death, Knife suggests as a strategy in the challenge that they all throw at one person- the "pathetic" Taco. Nickel seems uninterested and reluctant to participate in this strategy as seen by his aggravated expression, but does so anyway. Taco spits the rocks back at them, and Nickel says that they must jump over the rocks. He does so successfully, but Knife doesn't jump and is knocked off of his platform.