To even find the Octo Oven in Splatoon 2, you’ll first need to locate three Zapfish. Then you can head to the first Boss Kettle, where the boss battle is primed and ready to go. It is located near the middle of the Tentakeel Outpost area. Interacting with the kettle will get the party started.
As you battle the Octo Oven, your first order of business is to avoid its gluten-powered shots. Keep moving around so none of the loaves find their target, and watch for the Octo Oven to eventually crash to the ground in frustration. At that point, loaves should scatter everywhere and you can ink them so they’re safe to use as stepping stones.
Quickly climb toward the top of the area, while your foe remains incapacitated. That state won’t last long, and your goal is to get high enough before the effect wears off that you can target a tentacle in the middle of the oven. Blast it with your ink gun, which should deal damage to your foe but also send you back to lower ground.
Now the Octo Oven produces dangerous ink wells. They shoot purple into the air, which you need to avoid in addition to the standard attacks on the oven’s part. Watch for it to drop and send loaves scattering once more. Then repeat the process that worked the first time around, though doing so will be more difficult because there aren’t as many loaves to climb. Make sure to hurry, as before, or you won’t get to the tentacle in time to inflict any damage.
Once you have hit the tentacle a second time, you’re ready for the final round. Now the Octo Oven will rain ink from above, which you should avoid as you also steer clear of any other hazards. Eventually, you will have a chance to climb loaves toward the weak tentacle one final time, though they are shielded and you’ll have to make precise, quick movements to gain elevation quickly enough.
After you strike the weak tentacle a third time, you will defeat the Octo Oven and you can resume your journey through the world of Splatoon 2. There are still many challenges ahead of you, so don’t rest on your laurels quite yet!