Follow us on Twitter @LiquipediaSC2 if you'd like to be kept up to date on all things StarCraft II!

Bio (vs. Protoss)

From Liquipedia StarCraft 2 Wiki

Bio play refers to using an army that mainly consists out of Barracks units: Marines and Marauders.


A highly mobile and harass-based style of play. Uses a Marine, Marauder and Medivac opening (or MMM) for firepower and mobility in multiple pronged attacks to damage whatever is most appealing to the Terran and wear the Protoss down, while keeping an eye on the Protoss' early tech choice of Archon (use Ghost) or Colossus (use Viking) to keep control of the map and Protoss on the defensive and behind.

Unit Roles[edit]

  • Marine: With a high rate of fire but low health, without a health buffer like Bunkers or Marauders, Marines will not last long in even numbers against Zealots and Stalkers; but will increase in effectiveness as numbers increase quickly. Weak to area of effect attacks (Colossus)) and spells (High Templar unless these units are spread out and Colossus numbers need to be kept low or the splash damage makes Marine numbers impossible to maintain.
  • Marauder: Simply put the early game without Marauders is a purely Bunker-defensive one. With Marauders and Concussive Shells the Terran simply outclasses Stalkers and Zealots until Warpgate research completes. The firepower of Marauders into the mid and late game continues being strong against armored-units but need Marines for extra firepower against everything else.
  • Ghost: Highly expensive and should not be considered until at least two base economy is started. EMP acts as a grenade against Protoss shields and removes mana from spellcasters. It is a hard counter to both High Templar and Archons, but die just as quickly as Marines to colossus. The Terran needs to scout carefully to choose the correct numbers of Ghost to Vikings numbers to be able to attack Protoss head on.
  • Medivac: Healing Biological units and using dropship-based harassment and building sniping.
    • Extra Tips: Keeping large Medivac drop numbers accompanied with a Raven allows for an emergency PDD to cover hasty retreats should too many Stalkers/Phoenix be guarding the landing. Medivacs should unload troops while running away or move the higher health Medivacs back briefly to save the damaged ones, Air Armor is also highly recommended as well.
  • Viking: The strongest response to Colossus and Carrier preventing the range advantage abuse by gunning down two units with the Kiting technique. Produced until Colossus numbers are reduced to zero and used for little else afterwards.
    • If the Terran is caught off guard with either, two reactored-Starports, at least, will be needed to prevent Protoss death-ball status, and this is why Terrans prefer to actively dropship-harass the Protoss and snipe Tech, Sentries andStalkers to make the early game expensive for Protoss and delay Tech.

Supplementary Roles[edit]

  • Reaper: Weak in direct army battles, and thus are not commonly used until the late game when Protoss has to manage multiple bases and large army battles. With a low mineral cost but long build time, extra Barracks are required to maintain a task force of Reapers that can devastate expansions quickly. Attacking remote expansions will force Protoss to warp in army at remote locations, at which Reapers can runaway and attack a different location.
  • Banshee and Raven: Sometimes a Raven and Banshee (more DPS than Vikings but longer build time) combination is used instead of Vikings to deal with Stalker-heavy combinations, though a switch to Vikings is needed if the opponent has chosen to add Phoenix. PDDs and Banshee Cloak make it more difficult for Protoss to have a simple army composition that is strong against the Terran.
  • Battlecruiser: Sometimes used alongside Vikings and other air units as strong damage tanking units; the movement speed still remains an issue in contrast to bio though.


In the early game bio will lack the research to take Protoss head on without Marauders and scouting for 3 Gate, being active with your scouting SCV will allow you to spot potential proxy Tech (most commonly a Stargate for Void Rays or a hidden Dark Shrine). In the mid- to late-game you will need to scan or in some way scout the Protoss base as switching rapidly between producing Colossi and High Templars can make your unit composition less cost-effective.

If worried about the early game a 1/1/1 opening build is recommended as it can be used to respond to every tricky Protoss opening and transitions into bio later. Learning to do a safe fast expand and the necessary scouting is the other option but is much more advanced as there is not really a standard fast expand build order that cuts corners and covers it entirely.

Positioning and micro[edit]

You need to be careful about where to engage. You will face the difficult decision of what type of formation to take - if you clump your units together, you'll be able to deal with Zealots more easily, but if you spread them out, chances are Psi Storm and Colossi will be less effective. How spread out your army will need to be is something you'll mostly have to experiment with and adjust depending on your opponent's unit composition - the less Zealots he has, the more spread out your army can be.

A few simple rules can easily be applied:

  • Engage the Protoss when most of your troops are shooting, not just a few at the front; otherwise retreat and reposition the army.
  • Do not charge into small choke points unless you know the Protoss has no Colossi nearby or Storms available.
  • A wide arc/concave will benefit you.

In some situations the Protoss will be careless enough not to have an Observer in their army. Use a Scanner Sweep before engaging. If you see your opponent does not have an Observer, you can cloak a few Ghosts and EMP as many High Templars and Sentries as possible before attacking.

The first focus of a big battle should be to distract as many Zealots and Stalkers as possible and surgically take out High Templar and Colossi with whatever has enough firepower to do so:

  • Zealots: Move into feint and attack then run away from the opponent's Colossi/High Templar and the Zealots will follow allowing at least a few to be killed off.
  • Stalkers: Move in Ghosts in to attack the Colossi respectively. While distracting the splash units attack the Stalker numbers with everything else.
  • High Templar/Sentry: Scan the opponent's army and kill off any Observer with them. Move in with Ghosts and EMP any spellcaster clusters, if the EMPs did not hit properly separate Marine/Marauders into two or three groups and attack from different directions.
  • Colossi: In large numbers will need Vikings to reduce the numbers, but at 3 or less moving in Marauders to snipe them is also a strong option, just remember to run away from the rest of the army.

You also do not want your Vikings do be far in the front, since that will leave them open to Stalker fire. In an even battle, your Vikings will most likely die eventually, but you still want to make sure they deal as much damage as possible.

Medivacs are important to keeping your army alive, keep the ones with high mana in the back and ones with low mana in the front or use them for harass, do not lose too many though they only need a few in number to heal the army but are very expensive and fragile.


A pure Barracks-based army is only as strong as the upgrades it has to fight with.

  • Stimpack and Concussive Shells are a must to have any map presence.
  • Protoss units are high health and armor, thus a rush to the second attack upgrade is highly recommended.
  • Against a double Forge build attacking or harassing the these building is strongly recommended to delay the upgrades and put the Terran a head.