What the effects react to
Shields
Shield entities check whether a hero is Shielded, and grant stats or effects while the shield holds. 12 relics and items are built on it: 12 relics and 0 items.
Updated for patch 0.5.10
While a Shield holds
Three effects in this family only work while a hero is Shielded. Shield Fluctuator gives 20 Crit and 5 Mana Regen, up from 15 and 4 in 0.5.5; Shield Conduit gives 100 Attack and 100 Magic once 7,500 Shields have been applied; Shield Ascendancy gives +50% Defense and +50% Crit after 15,000. The smaller quests pay regardless, Shield Accumulator 15 Shards at 1,250 and Shield Vessel 30 Magic and 30 Attack at 2,500, and Shelter Mandate asks 30,000 for one more hero.
The lasting Shields in the family keep that condition on from the opening second. Shield Generator opens each fight with 400 on every hero and Shield Bauble with 250; Shield Bastion adds a lasting Shield worth 33% Max HP after Stall (15); Shield Investment Filigree spends a Shard at the start and after Stall (20) for 250 lasting Shields that grow by 50 each time it pays.
Retaliation
Shield Repriser returns 100% of the damage an enemy deals to a hero's Shields, Shield Fragmentation Engine 350%, up from 250% in 0.5.9. Shield Converter damages the nearest enemy for 50% of any Shield a hero receives from someone else, 33% before 0.5.2. Kits that shield only their owner, such as Kai's Resolute Strike or Rowan's The Protector, never set it off, while Fiona's Vault Spark does whenever it lands on another hero. Her spec The Lustrous adds a separate reply, burning whichever enemy deals damage to a Shielded hero.
Multipliers on both ends
Amulet of Shields adds 25% to the Shields its holder applies, and the Mystic upgrade Shield Magnification adds 50% to what its hero applies. Stall Tanks stacks both: the Amulet on Fiona and on Gustav, Shield Magnification on Gustav, and The Glacier turns his Blizzard, Defense-scaled Shields included, back onto himself. Kai's The Unstoppable is the only multiplier on the receiving end, 60% more Shields from all sources plus a share of his Attack. Enemies shield themselves too: Mushroom Tank gains Shields worth 10% of its Max HP every 10 seconds.
Relics and items that scale with Shields
Shield FluctuatorUniqueHeroes gain 20 Crit and 5 Mana Regen while Shielded.
Shield BaubleUniqueAt start of combat, heroes gain 250 lasting Shields.
Shield AccumulatorUniqueQuest: Apply 1250 Shields. Rewards: Gain 15 Shards.
Shield GeneratorCommonAt start of combat, Heroes gain 400 lasting Shields.
Shield VesselCommonQuest: Apply 2500 Shields. Rewards: Heroes gain 30 Magic and 30 Attack.
Shield RepriserRareWhenever an enemy damages a Hero's Shields, deal 100% of the damage back to the source.
Shield BastionRareAfter Stall (15), Heroes gain a lasting 33% Max HP Shield.
Shield ConduitRareQuest: Apply 7500 Shields. Rewards: Heroes gain 100 Attack and 100 Magic while Shielded.
Shield ConverterEpicWhenever a Hero gains Shields from any source but itself, damage the nearest enemy to them for 50% of the Shield applied.
Shield AscendancyEpicQuest: Apply 15000 Shields. Rewards: Heroes gain +50% Defense and +50% Crit while Shielded.
Shield Investment FiligreeEpicAt start of combat and after Stall (20), spend 1 Shard to apply 250 lasting Shields to all Heroes, then permanently increase the amount of Shields this applies by 50.
Shield Fragmentation EngineLegendaryWhenever an enemy damages a Hero's Shields, deal 350% of the damage back to the source.