This build has been tested on version 2.6.1 PTR, and in Season 12 on PC and PS4.
The adjustments to the Delsere's Magnum Opus set for the 2.6.1 have made it possible for a stable, durable melee range Wizard to once again hold up with the other set builds to take on tougher Torment and GR levels, albeit at a bit of a slower approach that highlights said durability over trying to blaze through Rifts as fast as possible.
The Delsere's 2 piece bonus allows for three of the four Signature Skills (Magic Missile, Shock Pulse and Spectral Blade) as well as Wave of Force, Explosive Blast, Arcane Orb, and Energy Twister to decrease the cooldown time of Slow Time by 3 seconds per cast, making the 15 second cooldown of the skill erasable with just 5 quick casts. The 4 piece bonus grants 60% damage reduction for the Wizard as long as least one Slow Time bubble is active on the field, with a 30% damage reduction to any allies within the bubble's radius, and the 6 piece bonus allows all enemies affected by Slow Time and for 5 seconds after exiting the bubble's radius to take 3800% more damage from the previously noted Signature Spells and Arcane spenders.
The melee oriented approach to the build utilizes stacking as much damage within a 15-20 yard range as feasibly possible while maintaining a solid defense and keeping the up-time on Slow Time maxed out to maintain the damage and damage reduction bonuses for the set. Ice Armor is the main defensive skill, granting a 12% melee damage reduction but more importantly with the Crystallize rune grants a 20% Armor buff for every melee attack received, stacking 3 times for a total 60% buff to Armor. For offensive skills, Arcane Orb utilizes the Arcane Orbit rune over the Frozen Orb rune here, instead with the emphasis on having enemies get in close cast it so it detonates right away and allowing the skill to be cast as normal instead of letting the four orbs linger. This stacks with the damage and damage range of Explosive Blast, using the Chain Reaction rune to get multiple blasts and the most damage total out of the skill, and is rounded out by the Arcane Torrent skill with the Arcane Mines rune, able to cast up to six at a time right in the perfect range of the Wizard to stack atop all the other skills' damage. Keeping Slow Time up as often as possible is key, so for the initial rune choice Time Shell is the best as it deducts 3 seconds from the total cooldown, making only 4 casts of any of the associated skills needed to cooldown Slow Time completely, which is easily managed.
The skills and how they work with the specific weapons and equipment help define how the build fights. Along with being easily able to distribute in close range, the Arcane Mines are able to stack in a small area to detonate against a single/multiple closely packed enemies for huge damage, making up the fact that they get no boost from the Delsere's set bonuses, and while channeling the mines the Wizard is still able to freely cast Arcane Orb and Explosive Blast without interrupting. The same is true with Spectral Blade, allowing the skill to chew through the cooldown of Slow Time while also synchronizing with the effects of Triumvirate to boost Arcane Orb's damage atop the Delsere's 6 piece bonus. The Barrier Blades rune casts health shielding for every use of Spectral Blade, stacking with the shielding from the killing of enemies with Dominance and the shielding from Molten Wildebeest's Gizzard for defense. Use of Slow Time itself with the Crown of Primus grants all the runes, adding greater Slow effects, Stun effects, attack speed and damage increases and additional damage reduction all in one cast. Simultaneous casting of Explosive Wave with the effects of Orb of Infinite Depth grants up to 4 stacks of 10% damage and 20% damage reduction, and paired with the effects of the Chain Reaction rune and the casting multiplier from Wand of Woh, should easily keep damage piled on enemies while maintaining the full 40% damage bonus and 80% damage reduction bonus. Add in the Ice Armor with the Crystallize rune for stacking up to 60% Armor on melee hits paired with the Halo of Arlyse granting up to 60% additional melee damage reduction and free casts of Frost Nova, and the Wizard has a staggering amount of damage reduction and defenses paired atop all that outgoing damage in melee range.
The passives are a balance of offense and defense, Audacity boosting all damage within 15 yards by 30% and Arcane Dynamo granting a 60% damage boost to a damaging Arcane spender skill after 5 successful casts of a Signature skill, easily done with Spectral Blades and adding even more damage to synch with all the other skill and item effects. Dominance and Unstable Anomaly are to boost defensive shielding and work to avoid fatal damage every 60 seconds, Dominance working upon killing enemies with extended absorption percentage and duration stacking for all the enemies coming into melee range. Galvanizing Ward is an alternative that grants stronger shielding, but requires 5 seconds without taking any incoming damage to activate which can be too long depending on the enemy spawns. It is of course a viable option to add if using a Hellfire Amulet, along with Blur for flat damage reduction and Unwavering Will for overall defensive increase and a slight damage boost when stationary, a sort of weaker catch-all version of the Traveler's Pledge/Compass Rose combination.
The variations on this build are a bit less drastic, mostly in terms of weapon options and a few of the skills. Unstable Scepter grants additional damage and a secondary explosion to Arcane Orb, further mitigating the damage loss from using the Arcane Orbit rune. The Fragment of Destiny helps make Spectral Blades a more viable offensive skill along with the boost from the Delsere's 6 piece bonus, granting another 50% attack speed boost and up 200% damage increase, which paired with the Shame of Delsere belt makes the skill execute lightning fast with higher damage, and with Barrier Blades that means much more health shielding. Another option to consider with that though is swapping the Barrier Blades rune for the Thrown Blade rune, turning the damage to Lightning with an increase to base damage percentage and range to 20 yards, making it even more viable for offensive use and getting even more out of the Convection of Elements for offensive capability.
A more defensive variation swaps out Arcane Mines to streamline the build heavily, replacing it with Diamond Skin with either the Diamond Shards or Enduring Skin runes, the former to mitigate the damage loss somewhat or the latter to prolong the damage absorption bonus. For stronger Greater Rifts however, the Crystal Shell rune to double the damage absorption percentage total might be a wise choice given how much more damage enemies will be dealing in a shorter span of time. The skill doesn't synchronize with any of the Delsere's set bonuses, but acts as a nice boost to defensive with all the other damage reduction and health shielding.
A more drastic alternative uses either Fragment of Destiny with the Winter Flurry Source, or the Source with the Rimeheart sword and the Ice Blades rune on Spectral Blade. Winter Flurry grants a 20% chance for enemies killed by Cold damage to release a Frost Nova, the Ice Blades rune using Cold damage, granting a Freeze chance on enemies and a boost to Critical Damage on those Frozen. The Rimeheart takes this a step further, using Cold damage itself as a weapon roll and the affix granting a 20% chance for Frozen enemies to be hit with 10,000% weapon damage. The Frost Novas from Ice Armor itself and moreso with Winter Flurry would facilitate this, and the Freeze chance from Ice Blades, again with a boost from Convection of Elements. Experimentation with the Ray of Frost skill with the Sleet Storm rune has also shown to work well with this last combination, the damage more evenly spread in a more consistent manner than with the burst damage from Arcane Mines.
While the 30% damage reduction for allies within the Slow Time bubbles does technically make for use in group play, the build unto itself is designed more as a solo build, lacking any other support/healing options and being much slower to move through enemy mobs.