Well designed. Especially with consideration to DR shields.
Having the ability only trigger on an unsuccessful attack makes the card more interesting and nerfs the skill to acceptable ranges.
Hope
Dusk Shield
Fog Shield
Diamond Shield (upped shield only)
Gravity Shield (requires +2hp)
Dissipation Shield
Bone Shield
Phase Shield
Sundial (I assume sundial works)
I do wonder if the Savage Temper is more of a Fiery attribute.
Updated Theory cost:
cost = 3
+1card = 4 = 3 atk (+3) + skill (+1)
cost = 2
+1card = 3 = 3 atk (+3) + upgraded (-1) + skill (+1)