Cheapest priced copy (Theros Beyond Death): $0.79 at Card Kingdom, near mint, their price list as of .
Mirror Shield 
Artifact — Equipment · Uncommon · Theros Beyond Death · #234
Equipped creature gets +0/+2 and has hexproof and "Whenever a creature with deathtouch blocks or becomes blocked by this creature, destroy that creature."
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.79 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Theros Beyond Death | 234 | Uncommon | $0.79 | $1.49 |
3 rulings from Wizards of the Coast
- 24 January 2020If a creature with deathtouch blocks the equipped creature and is then destroyed, the equipped creature remains blocked. Unless the equipped creature has trample, it won’t deal combat damage to the player or planeswalker it’s attacking.
- 24 January 2020The ability Mirror Shield grants triggers and resolves before combat damage is dealt. That creature won’t deal combat damage to the equipped creature or be dealt damage by it.
- 24 January 2020Once a creature without deathtouch has blocked or become blocked by the equipped creature, causing the other creature to gain deathtouch won’t cause the ability granted by Mirror Shield to trigger.