The Sizzling Key is a reward for completing main story objectives at the beginning of Grounded 2. Its description lists that it smells like cinnamon, but there's no indication of what lock needs to be opened by it. There is a hidden chest, however, waiting for the Sizzling Key to open it. This is where to find the Sizzling Key chest in Grounded 2.
How to Get the Sizzling Key
The Sizzling Key is acquired after you defeat the Mysterious Stranger in the Network Center top floor. Inside the Penthouse Office, you'll see the key on the desk to the right of BURG.L's head. Picking it up registers it as an important item, kept with your Collections. It will not appear in your inventory, so you don't have to worry about keeping it on you or possibly losing it if you die.
Where to Find the Sizzling Key Chest

The chest for the Sizzling Key is found in Pine Hill at the foot of a tree. The tree is on the second level of the region, not the very bottom, so you'll have to climb to reach the area. You're looking for a couple pieces of wood covering a space between tree roots. There's a rock and a group of pop gun ammo in front of the area. You can also slightly see a brown leaf on top of the wood pieces.

Head under the leaf and you'll find another group of pop gun ammo. Under that you'll see a blue shimmering light. This marks the buried treasure chest location. Dig it up (which requires the Tier 2 Omni-Shovel) to have a blue and gold chest appear.
Use the Sizzling Key to open the chest. You'll receive Spicy Glob x2, the only current way to get the resource required to make the Spicy Coaltana two-handed sword.
How to Craft the Spicy Coaltana

The Spicy Coaltana is a sword originally introduced in Grounded. Making its return with some modifications, you'll need to track down a couple rare ingredients to craft it.
To make the Spicy Coaltana, you'll need to have grabbed the recipe from the desk where you acquired the Network Center TURBO Optical Disk and the Sizzling Key. It requires the Spicy Glob x2 you obtained from the Sizzling Key chest, along with EverChar Coal Chunk x5 and Wolf Spider Chunk x4. The coals can be found around and inside the fire pit by hammering Charcoal, which requires the Tier 2 Omni-Hammer upgrade.
When you have all the materials, go to the workbench to craft the Spicy Coaltana. It deals Spicy damage as well as Slashing, making it useful against Orb Weavers. It doesn't require any special upgrade materials, so you can use the Brittle Whetstone to boost it to level 3.
Now that you have the Sizzling Key, check out more guides below: