Diablo 4 Ghostly Ashes Guide (Part 2): Best Boss Skills to Prioritize Upgrading

In the D4 items our Spectral Ashes guide, we covered how to farm this valuable resource and where to use it. Now, let’s focus on what to spend it on. With dozens of Boss Powers available in Season 8, choosing which ones to upgrade first can make or break your build. This blog will help you prioritize the best early-to-midseason upgrades for your class.

Understanding Boss Powers

Boss Powers are temporary yet powerful enhancements tied to the seasonal Apparition Incursion system. Each power has a rarity tier (Magic, Rare, Legendary) and can be upgraded up to rank 20 using Spectral Ashes.

Every power offers class-specific benefits or gameplay enhancements, such as increased resource generation, AoE boosts, crowd control, or cooldown reductions. When upgraded wisely, they can elevate your entire build.

General Advice: Upgrade Strategy

Here’s a simple framework to guide your upgrade path:

Focus on Synergy: Pick powers that enhance your main skill rotation.
Early Impact: Invest in powers that immediately improve survivability or damage.
Avoid Spreading Too Thin: Choose 2–3 core powers and level them aggressively.
Watch the Scaling: Powers that scale with rank (not just tier) are often worth upgrading sooner.

Best Boss Powers for Each Class (Starter Recommendations)

Barbarian

Top Pick: Crushing Resurgence

Effect: Increases damage after using a Shout.
Why: Barbarians rely heavily on Shouts for survival and burst. This power greatly enhances synergy in both solo and group play.

Also Consider: Frenzied Devastation (boosts Fury generation)

Sorcerer

Top Pick: Volatile Conduit

Effect: Lightning spells deal splash damage to nearby enemies.
Why: Works excellently with Chain Lightning builds, creating deadly AoE synergy.

Also Consider: Mystic Efficiency (reduces cooldowns of Defensive skills)

Druid

Top Pick: Nature’s Echo

Effect: Casting an Earth skill gives you free Storm skill damage.
Why: Hybrid Druid builds thrive on mixing Earth and Storm. This power increases your output with minimal resource use.

Also Consider: Feral Endurance (damage reduction after Shapeshifting)

Rogue

Top Pick: Precision Ambush

Effect: Increases Critical Strike Damage after using Stealth.
Why: Rogues benefit from quick burst kills; this power synergizes with Trap and Imbuement builds.

Also Consider: Deadly Momentum (attack speed buff on crits)

Necromancer

Top Pick: Grave Reaping

Effect: Minions explode on death, dealing AoE damage.
Why: For Minion-focused Necros, this creates a feedback loop of destruction that wipes packs fast.

Also Consider: Bone Tyrant’s Hunger (buffs Bone skills when a corpse is consumed)

Priority System: Rank Investment

Upgrading a Legendary power to Rank 6 costs over 100 Ashes, so think long-term:

Ranks 1–3: Low cost, good ROI. Upgrade early.
Ranks 4–10: Moderate cost. Choose powers that are central to your build.
Ranks 11–20: High cost, high commitment. Reserve for late-season optimization.

Pro tip: Get your core offensive power to Rank 6–8 quickly, then balance with defensive or utility powers.

When to Stop Upgrading

You don’t always need to hit Rank 20. Some powers have diminishing returns after Rank 10 or 16. Keep a close eye on diminishing percentage gains. If your next upgrade costs 400 Spectral Ashes and gives you just a 2% improvement—pause and reconsider.

Spectral Ash Management

Wasting Spectral Ashes on fringe powers can slow your progression. If you’ve picked up powers that don’t synergize with your current build:

Don’t upgrade them.
Save Ashes for a power reset or for newly unlocked powers at higher tiers.

Note: Blizzard may introduce a “Boss Power Reroll” system in a future patch. If so, this would give players flexibility with their Ash usage, so watch patch notes closely.