Colossus

The Colossus is one of the few things in Stellaris capable of permanently reshaping the direction of a playthrough the moment it’s used — a devastating weapon capable of resolving a target planet in catastrophic fashion, but at the near-certain cost of provoking every other empire.

Unlock and build requirements

Unlocking the Colossus requires taking the Colossus Project ascension perk, then completing the special project it opens up — you’re prompted to choose your starting weapon when that project is halfway done, and can research and retrofit other weapon types later via the ship designer. Building one also requires a Citadel with Capital Assembly Yards (or a Mega-Shipyard), and you’re limited to one at a time (though it can be rebuilt if lost).

Confirmed weapon types include the Global Pacifier, which irreversibly converts the target into a Shielded world, and the World Cracker, which destroys the planet outright — different weapons carry different opinion penalties with other empires, and some have unique story consequences (using certain weapons on a Holy World, for example, can wake the Holy Guardians and trigger an immediate war).

What to consider before using it

• Diplomatic cost: using a Colossus will almost certainly tank your standing with every other empire, potentially triggering a large-scale coalition against you.
• Irreversibility: the effects are typically permanent. Make sure this is genuinely the strategic tool you need for this playthrough before pulling the trigger, not a snap decision.

When it’s actually worth considering

For dealing with an extreme threat (specific story branches, or if you’ve already committed to a “galactic scourge” playthrough), the Colossus can be an extremely high-value option. For a standard playthrough where you care about normal diplomatic relations, exercising restraint is the safer call.