Malamar is not immune to Taunt for one. Not sure what made you think that. And although I questioned it myself at first, Vigoroth has a decent shot at beating Malamar in theory.I can't see vigoroth beating malamar, especially when malamar has a super effective move that boosts its stats, and is immune to taunt. Tbh although vigoroth has nice bulk, it just gets forced out right as it starts to set up, and you're just better off using something like gurdurr, malamar, or even quagsire as a bulky physical mon
+6 4 Atk Malamar Superpower vs. +6 252 HP / 0 Def Vigoroth: 194-230 (53.2 - 63.1%) -- guaranteed 2HKO
That's if you Knock Off along the way of setting up. Okay consider these facts now. Malamar has 8 Superpowers. Malamar comes in on Vigoroth (you're not going to switch in to try and set up on a Superpowering Malamar). This is the damage Malamar can inflict after a Bulk Up as you come in, then another one before you hit this Superpower:
4 Atk Malamar Superpower vs. +2 252 HP / 0 Def Eviolite Vigoroth: 66-78 (18.1 - 21.4%) -- possible 5HKO
You easily set up to +6 and Slack Off any damage if needed. Superpower runs out quickly, Knock Off does this much after Eviolite is gone:
+6 4 Atk Malamar Knock Off vs. +6 252 HP / 0 Def Vigoroth: 79-94 (21.7 - 25.8%) -- 2.1% chance to 4HKO
Return does this much:
+6 4 Atk Vigoroth Return vs. +6 252 HP / 0 Def Malamar: 102-121 (27.1 - 32.1%) -- 54.3% chance to 4HKO after Leftovers recovery
Vigoroth has Taunt which stops RestTalk. It will take a while, but in theory Vigoroth wins, not counting crits of course.
Also the arguments "it gets forced out right as it starts to set up" and "use gurdurr instead" are not particularly convincing, just letting you know.