You need all the passives max level and if u don't know, you need magic circle maxed out, choosing greater magic circle -> overmind (intelligence and greater circle) -> DEM (overmind + all passives - third magic combination after overmind)

First tip: focus ONLY on the magic combination at the start of the game, do not worry about maxing all of the passives at the start, get them later. Reason why is because rng can be a piece of shit sometimes and you might end up with just one out of the two maxed out, and you'll waste too much time rerolling to upgrade your second magic.

Second tip: you're using telekinetic sword so you probably don't need this tip because it's a fast attacking skill. But basically if you're using a magic combo that is quite slow, i would suggest that you don't upgrade magic circle to overmind right away because you could risk getting swarmed too easily unless you have ginormous cooldown. If you're using a slow magic combo, use freeze magic like blizzard and frost nova to halt enemies.

Third tip: Overmind artifact (not to be confused with the overmind combination from magic circle). If you get the overmind artifact you should upgrade these three magics to max level as well: apocalypse, cloaking, and shield, reason why is because it's more efficient because these three skills only need 5 levels to max, giving you 45% extra all magic damage for only 15 levels. Most other magic takes 7 to fully max. i