I like the random damage reduction, but to get D5-3 for 2 quanta seams a bit to expensive.
If we use the D4-1 and D6-1 as a passive effect, its places the card solidly in the shield category. I wonder if it would be possible to code it so the opponent could see the new damage reduction value each turn. What about a variation on the -2, -1, 0, +1, +2 theme. Active ability Gamble (no cost): Target creature permanently gain -2, -1, 0, +1 or +2 attack strength.