The Ominous Trail is a quest in Chapter 17, "Deliverance from Chaos" in Final Fantasy VII Remake, taking place in the Shinra Building. Cloud Strife, Tifa Lockhart, Aerith Gainsborough, Barret Wallace, and Red XIII investigate an ominous purple trail left from Professor Hojo's laboratory.
After using the elevator, follow the purple trail across the floor to the executive suite on the 69th floor, up several flights of stairs up to the President's Office on floor 70. A voice can be traced to an exit on the right. Approaching him will lead to a cutscene and a boss.
Jenova Dreamweaver boss
Jenova Dreamweaver can use a ranged attack telegraphed across the floor which inflicts Stop. It has no elemental weaknesses, but its left and right tentacles are its weak spots. Aerith should stay back and support the party, while Cloud and Tifa cripple the tentacles with character abilities and Tifa's Unbridled Strength techniques can be used to pressure it. Though Summoning Materia can be used, it is best saved until the final phase.
After losing 20% of its HP, Jenova will use Rejection and Mourning Wail, repelling melee attacks and dealing damage. Switch to Aerith and use her to hit the boss from a range with attacks and spells amplified by Arcane Ward, while dodging its attacks. Once Mourning Wail ends, switch back to Cloud and Tifa and attack the tentacles. To move in quickly, close the gap with Cloud's Focused Thrust and Tifa's Overpower. Later in the fight, it becomes immune to magic, meaning Cloud and Tifa must attack the tentacles while Aerith provides support.
After losing 50% of its HP, the boss will create several more tentacles at a distance and become immune to damage. The tentacles must be destroyed, and are best destroyed with Tifa due to her movement speed and combos. Defeating them raises Jenova Dreamweaver's stagger gauge, and after a wave are defeated, it will temporarily become vulnerable to damage until more tentacles appear, meaning Cloud should use Punisher Mode and build its stagger gauge further. Keep destroying the tentacles and getting in damage until it is staggered, then use Tifa's martial techniques with Unbridled Strength to increase the damage it receives, and use any limit breaks.
Once it is reduced to 25% HP, Jenova Dreamweaver will teleport away. Follow it to continue attacking with Cloud and Tifa, and when it engulfs itself in energy, pull back at a distance and switch to Aerith. Defeat all tentacles that appear when Jenova becomes invincible, and when it is vulnerable again, cripple its left and right tentacle, and follow it wherever it teleports.
Hard mode tips
Against Jenova Dreamweaver, Aerith should use Lightning Materia paired with MP Absorption Materia to cast spells in an MP-efficient way. Time Materia is best used to counteract its Stop by pairing it with Warding Materia. Magnify Materia should be paired either with Barrier Materia or Healing Materia. As with most hard mode battles, casting Regen provides a good MP-efficient form of healing. Parry Materia is also useful on Tifa to provide much-needed mobility to escape many of Jenova Dreamweaver's attacks. Elemental Materia can also be paired with Fire Materia to absorb some of its fire-based attacks.
The later phases of the battle are more challenging. Prayer Materia provides an MP-efficient way to heal, and if Refocus Materia is used (preferably with Spectral Cogwheel on Aerith and Transference Module with Tifa), ATB bars can be filled quicker, allowing it to be used more easily.
Defeating Jenova Dreamweaver will reward Tifa's Way of the Fist Vol. XIV.