Bloodmagic is a Resource that increases damage 200% of your missing HP% while doubling the cost of Skills. Bloodmagic uses HP as a Resource. MP becomes HP with Bloodmagic. MP on Hit and Regen replace HP instead. Bloodmagic Set affix can be rolled with Amethyst or placed as a Mythic affix on any Item. they do not stack if you use both.
MP Reduce +40% is an Epic affix that can be placed on the MH, OH, or both. it reduces the mana cost of the Skills on the weapon that MP Reduce is placed on.
I recently did a test and found out that these can be used together. with Bloodmagic on a test build with MP Reduce on my MH weapon, the Skill costs for the MH were reduced by 40% before being doubled by Bloodmagic. the Skill costs for the OH were not reduced.
the reason I did this test is because I always have problems with running low on HP when using Bloodmagic. I’m sure that with testing, I could find a balance that lowers the HP slowly to take advantage of the extra damage without running out of HP before the enemy is dead. using MP Reduce makes it easier for me to use Bloodmagic, but now I just need to make a build with both of them to see if it works as good as I hope they do.