The answer to this is often including ramp spells that aid and even quicken the generation of mana in a Commander deck
So as far as strategy goes, since Dusclops is a Basic Pokemon card with a Stage 1 evolution in Dusclops, and a Stage 2 evolution in Dusknoir, which I'll be reviewing the next couple of days, you'll more than likely want to use some of those Pokemon with this card, however, since I have not reviewed any of those cards yet, I will just act like Duskull does not have any evolution forms and that it will be used on its own
The wording allows you to either generate a second copy of the same creature from your deck, or grab a completely unrelated creature which happens to share the same total stats
The fun comes from finding ways to use their sacrifice and discard themes to fuel engines that drain your opponents while you keep your board strong
So long as you sacrifice a land while casting Constant Mists, you get to put the spell back into your hand after it resolves