In DMC1, all you have to do is get abunch of red orbs and buy everything you can at the shop. There is a limit to how many items you can buy, but other than that your inventory is infinite. Keep on playing normal mode and farm the untouchables, you should get It hink about 3 per playthough. Keep on doing it until you get 40ish, and then play DMD. Super easy.
In DMC3....infinite devil trigger costume+Quicksilver. You win.
Then again, I never did these because I was too pro to do em.
Does this game have super easy ways to beat DMD mode? Well IDK because H&H mode is beast.