Annihilus is a Unique Horadric Seal reported to drop from the Echo of Uber Diablo, which may appear after a World Boss in Diablo 4 Season 15. Stay in the arena after the boss dies and watch for the "Diablo walks the earth" alert; the Echo does not appear after every encounter. Some players keep routine purchases separate from the hunt with D4 Gold, but the reported Annihilus route still starts with a World Boss.

Reach the possible Echo spawn

There is no confirmed guaranteed trigger or vendor exchange for Annihilus. The practical preparation is simple: pick a difficulty your character can handle reliably, arrive before the World Boss fight ends, and stay nearby afterward.

Check the in-game World Boss timer and travel to the marked arena before the encounter ends. Do not leave the fight until the boss is defeated.
After the kill, remain in the arena. Watch for the "Diablo walks the earth" message and a follow-up appearance of the Echo of Uber Diablo.
If the Echo appears, engage it promptly and stay in the area during the fight. Defeat it, then inspect the drops and your Talisman inventory for Annihilus.
If there is no alert or follow-up enemy, continue playing and try another World Boss. A missing spawn does not mean you missed a quest step.

The alert is the useful confirmation that the reported follow-up encounter has begun. No alert means there is no confirmed Echo to fight, so repeatedly checking the arena or changing your build will not turn that attempt into a guaranteed spawn.

Compare Annihilus rolls before filling Charm slots

Annihilus occupies the Seal slot, not a Charm slot, and unlocks six Charm slots for your other Talisman pieces. That lets you plan around its Seal bonuses without giving up room for set pieces or a Unique Charm such as Hellfire Torch.

All Stats: +10% to +20%. Higher rolls can support a build that benefits from broad stat bonuses.
Resistance to All Elements: +10% to +20%. Favor a stronger roll if your character needs more elemental defense.
All Skills: +5 to +10. This is the standout line to compare for a skill-focused build.
Bonus Experience: +5% to +10%. It can help while leveling; at endgame, weigh it against the combat value of another Seal.

Check the complete tooltip when comparing copies; do not assume every Annihilus rolls at its maximum. Then arrange the six Charm slots around the set bonuses your build needs, leaving room for any Unique Charm you want to equip. A Sorcerer or another skill-focused character may value All Skills highly, while a set-focused build should compare Annihilus against the effect of its alternate Seal before committing.

Season 15 Horadric Cube recipes can reroll eligible base affixes on Charms and Seals. Check the recipe preview and material cost before using one: a reroll does not change a Unique power or a Seal's set bonuses, so do not spend materials expecting it to repair those effects.

Avoid missed drops and unreliable leads

Leaving as soon as the World Boss falls is the main practical mistake. Stay in the arena for the possible alert, and check that your loot filter displays Unique Seals so Annihilus is not hidden among other drops.

Do not treat a Stone of Jordan salvage count as a confirmed spawn requirement, and do not expect every World Boss to produce the Echo. Annihilus is a separate endgame hunt, not a Reliquary reward or a known crafting recipe.

Before the next World Boss, check which Annihilus roll your build needs, choose a manageable difficulty, and arrive at the marked arena early. For a separate option when budgeting routine purchases, cheap Diablo IV Gold is not a requirement for the drop; stay for the post-boss alert and inspect your Talisman inventory afterward.