Mirror

Mirror
The mirror can be found in the restroom in Ten-Mou, in a house at the Graveyard Sea, in the washrooms inside Ocean Lab, in the washroom in Robber's Fate, in the washrooms in Dying Mall, in the bathrooms in Frozen Edge, and in the Guardian.

Mirror Shard
The mirror can be broken into pieces with the delete hammer which gives the Mirror Shard tool that starts with 4 shards. Each additional mirror smashed will grant 4-5 more shards. The Mirror Shard's purpose is to teleport the user into their own net dimension. Every time it's used, it uses up 1 shard. If the Mirror Shard has no shards left, it can be refilled by smashing another mirror.

Also, you can get more than just 4 shards from a mirror. Pieces of broken mirrors can be broken multiple times before the broken pieces despawn; sometimes you can get up to 28 shards from one mirror. The Mirror Shard cannot be used when the user's net is empty, instead displaying a message that it cannot be used.