[RPG] What are the implications of the Dual Implement Spellcaster feat

Yes, a pact blade implementified, dual implement spellcasting hexblade double dips on enhancement bouns damage

Dual Implement Spellcaster's^DDI buff requires that you wield a magic implement in each hand, that both implements be usable with the power, and that you must be capable of wielding both implements.

If we assume that by some means light blades have been learned as an implement type (for example via swordmage multiclass) then a fey-pact hexblade could wield their Blade of Winter's Mourning^DDI as an implement.

Since manifesting the Blade of Winter's Mourning requires that the hexblade hold an implement in one hand, the hexblade now has an implement they are capable of wielding in either hand. And as long as the power being used is (a) an implement power, and (b) not an implement power for another class gained in a way such that the "usable with the power" clause is not violated all the requirements of Dual Implement Spellcaster are met.

The only question remaining is does the Pact Weapon class feature somehow deny this combination. The only relevant passage appears to be:

Your pact weapon shares your implement's enhancement bonus, critical hit effect, properties, and powers.

You could argue that since the pact weapon shares the implement's enhancement bonus, it can't stack with the implement, but since a double weapon's enhancement bonus can be made to stack with it's self I don't see a problem here.

The word between the number and the bonus is important. For each unique type, take the highest. If there's no word, add them. Be careful of the wording of bonuses, many of them changed when essentials came out to make them more compatible with weapons expertise.

If you have a +2 racial bonus to arcana, a +3 item bonus to Arcana, a +4 item bonus to arcana, then you have a total of +2+max(+3,+4)=+6 bonus.

Example 1: Hellfire blood has no word between the number and the bonus, so it adds to everything. Using a fire keyword power, in heroic, you get a +2 to attack: +1 feat, +1 untyped.

Hellfire blood:

Hellfire Blood Heroic Tier Prerequisite: Tiefling Benefit: You gain a +1 bonus to attack rolls and damage rolls when you use a power that has the fire or the fear keyword.

The confusion over this feat stems from the Feb 2010 errata:

Update (2/8/2010) On the Benefit line, delete “feat.” This change ensures that this feat continues to provide a benefit despite changes to the Weapon Expertise and Implement Expertise feats.

Example 2: Total +4 to arcana checks.