A 100% MoM character has been possible for the past couple league in standard but I couldn't afford it (double PC rings, weapon trees). Now with the MoM from TWWT, it's much easier to achieve 100%.

PoB: https://pobb.in/vVOA7r9lfpfd

The build focuses on mana and recovery, notably recoup and the regen from TWWT. For additional mitigation, the build uses Chaos Inoculation and Divine Flesh. The biggest weakness is the lack of physical mitigation. The damage is low but consistent at around 1.5M boss dps (1/3 from RF). This is sort of a meme build but it can actually do content. I use the current version (90% MoM) for heist and some afk bossing (limited pinnacle bossing, clip); it's lacking the dps for Simulacrum.

Stats

Mana: 16 500

Mana regen: 20 100 (120%)

Mana recoup: 172%

Resist: 76/78/77

Suppress: 44%

Mechanics

MoM - Mind Over Matter: 40% Keystone, 21% Body Armour, 11% Aylardex, 10% Ascendancy, 10% Watcher's Eye, 5% Helmet Corruption, 3% That Which Was Taken. 100% MoM enables ignoring life but takes a lot investment which limits the build possibilities.

Aylardex: grants MoM per Power Charge (4 base, 4 tree, 1 aylardex, 2 malachai's loop)

Chaos Inoculation: grants immunity to chaos but limits the amount of auras.

Divine Flesh: grants 50% less elemental damage taken. As the build doesn't invest in ES, there is no downside.

Eldritch Battery: disables the inherent stun avoidance from ES.

Recovery Rate: very important as it scales all recovery sources (regen, recoup, etc).

Tattoos: gives 40% recovery rate, 1 PC, 16% mana, 480 mana (and more). The PC is especially important, otherwise a PC ring is required (or weapon tree). Warrior's Tale is necessary to double the recovery rate.

Ralakesh's Impatience: gives permanent charges, replaces min PC Grand Spectrums (for mana Grand Spectrums).

Flagellant's Flasks: automates utility flasks.

Options: Penance Brand of Conduction + brand Mastery to recover mana (up to 100%/s). Spirited Response with the new Call to Arms. Reserving life instead of using CI.

Gear

Body armour: legacy 21% MoM

Helmet: legacy 5% MoM

Aylardex: max res corruption

Belt: mana recovery rate stygian vise (recoup jewel)

Rings: % mana and recoup

Weapon: mana regen, crusible tree with more mana (I really regret not getting PC), abyss socket (recoup jewel)

Malachai's Loop: gives 2 PC (a ring would be better)

Jewels: Watcher's eye (Clarity), TWWT, Transcendent Mind, Grand Spectrum, Warrior's Tale, Healthy Mind, Pure Talent, Voices, Glorious Vanity

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Upgrades

Finish crafting the scepter. Craft a 2 PC ring with recoup then craft a second scepter. Craft a new belt with flask mods.