The Boost Guardian
|Featured in||Metroid Prime 2: Echoes|
|Location||Dark Torvus Arena, Dark Torvus Bog|
|Attacks||Boost Ball, dark energy|
|Weakness||Light Beam, Morph Ball Bombs, Super Missiles|
The Boost Guardian has several different attacks. It has the typical abilities expected of a Warrior Ing—slashing, possession, energy beams, and amorphous transformation. In addition, it can also summon Inglets while in puddle form and boost around the room in the form of a spherical ball. In this latter attack, it can destroy any of the four pillars within the arena as well as any Inglet with which it comes into contact.
There are two phases within the battle, the first fighting it as a regular Ing and in its Boost Ball. While in the second phase, the Ing will constantly boost around the room and move about as a puddle. During this time, the Guardian is only vulnerable to Morph Ball Bombs, but immune to any damage. After some point, it will return to phase one.
- The Boost Guardian is physically identical to the Jump Guardian, the only other Guardian Ing to be fought in its natural state.
- If Samus damages the Boost Guardian with a bomb while it is in its ball form, it will immediately revert to its puddle form.
- The Boost Guardian is widely considered to be one of the most difficult bosses in Metroid Prime 2: Echoes. This is due to several factors:
- The player will only have a few energy tanks at the time of the battle, even if they've found every tank possible.
- The Boost Guardian's Morph Ball form is invulnerable and capable of dealing heavy damage with its Boost Ball (approximately 50 units with the Dark Suit and 100 with Varia in the GC version - this was toned down in the PAL and Wii versions). Although it can be forced out of the form with a Bomb, its speed and power can make this a difficult task.
- The lack of Light Crystals or Beacons forces Samus to take constant damage throughout the battle, and health recovery is difficult (the pillars are destroyed erratically, and taking the time to defeat Inglets can leave Samus vulnerable to other attacks).
- The Boost Guardian is fought in a small room with the only available cover - the four pillars - being easily destroyed by the boss's Boost Ball and the puddle forms of the Boost Guardian and its summoned Inglets taking up a lot of the floor space.
- Bryan Walker, senior director of development at Retro Studios, claimed that he was never able to defeat the Boost Guardian without going into debug mode. 
- The Boost Guardian and the Spider Guardian are noticeably easier in Normal Mode of New Play Control! Metroid Prime 2: Dark Echoes and Metroid Prime Trilogy.
- The Boost Guardian is the first Ing boss that Samus fights without any accessible Safe Zones. Quadraxis was the second and the Emperor Ing was the third (although by that point Samus has the Light Suit, so Safe Zones are not as imperative). Dark Samus' third battle is also fought without any Safe Zones, although she is not related to the Ing.
- In the data of the Metroid Prime 2: Echoes Bonus Disc, the Boost Guardian is named the Boostlet, and is described very differently than its final form.
|Ruling caste||Emperor Ing|
|Battle forms||Warrior Ing • Hunter Ing • Boost Guardian • Jump Guardian • Ingstorm • Darkling Tentacle|
|Submissive||Darkling • Inglet • Ing Webtrap • Flying Ing Cache|
|Immobile||Bladepod • Ingsphere Cache • Ingworm Cache • Ingworm • Webling • Ingclaw|
|Misc||Black fog • Ing Horde • Ing Larva • Fusion attack • Transdimensional energy • Phaz-Ing|
|Species|| Alimbic • Boost Guardian • Chozo (Ghost) • Craftsmen • Dark Pirate Commando • Darkling • Darkling Tentacle • Gorea • Ing (Hunter, Emperor, Warrior) |
Ingsphere Cache • Kralee • Leviathan • Luminoth • Metroid Prime (Core essence) • Phantoon • Warp Hound • Phazon Metroid
|Gateways||Alimbic Cannon • Artifact Temple • Interdimensional void • Portal • Stronghold Portal • Wormhole|
|Alternate Dimensions||Dark Aether • Infinity Void • The Locker • Oubliette • Stronghold Void|
|Other||Black fog • Dark Visor • Darkburst • Multidimensional Stealth Warship • Transdimensional energy • Transdimensional flux|