Can you cast sanctuary on yourself?

Unless otherwise specified, you can cast any spell on yourself.

I wonder if this would work on my imp or owl, any time they try to kill it, they have to pass a WIS check to do so, extra layer or protection.  Plus, if I have Spirit Guardians and Armor of Agathys on, then if it were melee characters trying to cut it down, they're forced to attack me instead, and suffer Spirit Guardian and Armor of Agathys damage...?

If using a continuous damage spell before this spell, was it still active?

At my table, I'd rule that if the continuous damage is automatic, requiring no action on the part of the caster, it continues as usual, but if it requires an action, bonus action or reaction to inflict the damage each round it would be subject to the Wis save.

The opponent isn't forced to continue the attack, only choose a new target or lose it. So they could voluntarily lose the attack to avoid the effects of your spells.

Also, as written it doesn't affect AoE spells (as they're not "targeting" an individual creature), so there's still a vulnerability. However, being a bonus action and non-concentration spell, it's incredibly powerful when used on a tank character (or, in my case, a heavily armoured Artificer Gnome with Shield stocked for any attacks which did succeed).

Is the mirror destroyed upon use of the spell? 

Spells that consume materials will always say if the material is consumed during the casting

Lets say I have already cast spirit guardians and spiritual weapon then I cast sanctuary on myself. Would the damage from my spirit guardians or my spiritual weapon cause sanctuary to end?

I'd say no because it's the spirits making the attack, not you. It says if the warded creature makes an attack. 

I was thinking the same thing about spiritual weapon, it says "you make an attack" so that would end the sanctuary due to you, attacking, and then dealing damage to another creature.

"You create a floating, spectral weapon within range that lasts for the duration or until you cast this spell again. When you cast the spell, you can make a melee spell attack against a creature within 5 feet of the weapon. On a hit, the target takes force damage equal to 1d8 + your spellcasting ability modifier."

I think it would. Per the spell description: If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends.

The Spirit Guardians is a spell that was cast that (continues) to affect an enemy.

i would ask the same for the Artilerist artificer. you can command your turret to attack that with the ballista it says to make a ranged spell attack, flamethrower is a save against your spell DC. Its using your stats but that could be related to your ability to modify it and how it improves with you. If you had a companion like beast master or a battle smith would having them attack be the same? i think its up to the dm on that part. You could be a druid that casts spike growth in front of an enemy to make them have to go around whial under the effects of sanctuary then the DM could have them walk into it and take damage and say you no longer have sanctuary because your spell hurt them. My thoughts on spiritual weapon vs the cannons/ class pets is that the spiritual weapon can not be attacked and you must use verbal and somatic components to cause it to swing and hit them, the cannon/ class pets have HP and same as you telling your allies to attack, they are the source of the damage, for the cannon it follows commands mentally so it would be hard to say that you were doing the attack (unless you were holding it maybe).

Yes you can

Quote from Mr_Pockets >>

i would ask the same for the Artilerist artificer. you can command your turret to attack that with the ballista it says to make a ranged spell attack, flamethrower is a save against your spell DC. Its using your stats but that could be related to your ability to modify it and how it improves with you. If you had a companion like beast master or a battle smith would having them attack be the same? i think its up to the dm on that part. You could be a druid that casts spike growth in front of an enemy to make them have to go around whial under the effects of sanctuary then the DM could have them walk into it and take damage and say you no longer have sanctuary because your spell hurt them. My thoughts on spiritual weapon vs the cannons/ class pets is that the spiritual weapon can not be attacked and you must use verbal and somatic components to cause it to swing and hit them, the cannon/ class pets have HP and same as you telling your allies to attack, they are the source of the damage, for the cannon it follows commands mentally so it would be hard to say that you were doing the attack (unless you were holding it maybe).

 

 An important distinction is "casts a spell that affects an enemy"; not damages, just affects. So, the Friends cantrip would end Sanctuary. I'd say in that respect, Spike Growth would be a DM call. Is altering the battlefield affecting your enemy?

As for companions and pets, I'd say you're safe RAW. As long as they're not the warded creature, they aren't affected by the spell, so could also still be attacked without penalty.

If someone was attacking you in melee with a melee weapon and failed their save, they must chose a new target, but if their new target is 20ft away and they have no reach, can they use their movement to go and attack that target or do they lose the attack?

A "Divine Soul" Sorcerer using "Sanctuary" and "Shield" can become quite difficult to target...

Enemies would have to risk a Wisdom-saving throw just to have a chance to target the sorcerer...and if they do, the sorcerer could just use "Shield" to block most harmful blows.

Pulling this off, even once, creates a unspoken deterrent for conventional attacks.

I would even consider multiclassing a level of "Divine Soul" sorcerer with perhaps a Lore Bard...creating a character who laughs and intimidates enemies, daring them to hit them while demoralizing them.

With a slew of support spells like "Faerie Fire" or "Healing Word", plus Bardic Inspiration, the bard can still contribute each turn without breaking "Sanctuary".

Yes

As you cast sanctuary, your eyes widen and become unbearable cute. As the orc swings its axe towards you, it stops, unable to harm such a adorable thing. You have now invented magical puppy dog eyes.