The Boost Guardian has several different attacks. It has the typical abilities expected of a Warrior Ing—slashing, possession, energy beams, and amorphous transformation. Its main attack is unleashed a few moments into the battle; it can 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. If a pillar is destroyed, an Ultra Energy orb and an Inglet will appear in its place. Inglets otherwise spawn throughout the battle, which also succumb to the Guardian's boost attack should it come into contact with them.
There are two phases to the fight: the first involves fighting the creature as a regular Ing and inflicting damage, while the second has it utilize its Boost Ball form. Phase one is straightforward, but after a while it will transform and begin the second phase by boosting around at various speeds. While preparing to transform, the creature is immune to any attack. After three consecutive boosts, it will revert into a puddle and move about. During this time, the Boost Guardian is only vulnerable to Morph Ball Bombs. While boosting around, should the creature hit a pillar, or should Samus strike it with a Bomb, it will also transform into its puddle form. Eventually, it will return to phase one; a cutscene will play and Samus will be forced out of Morph Ball. The creature can become amorphous during this time as well, where it can still be damaged, but cannot be defeated until it becomes solid again.
Morphology: Boost Guardian
Boost-powered Warrior Ing. Boost Ball ability grants great speed to enemy. Target can only be damaged in solid form. Find a way to keep it solid.
This Warrior Ing has absorbed the power of the Boost Ball. It can boost-blast toward its enemies, using its body as a potent weapon. When it is not in solid form, engaging it in Morph Ball mode may provide better attack opportunities.
The Boost Guardian is widely considered to be one of the most difficult bosses in Metroid Prime 2: Echoes, due to several factors. First, Samus will only have a few Energy Tanks at the time of the battle, even if she has acquired every possible tank up to that point. Second, 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 take up a large amount of floor space. Third, the lack of Safe Zones 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. Finally, the Boost Guardian's Morph Ball form is invulnerable and capable of dealing heavy damage with its Boost Ball (approximately 45 units on Hard/Hypermode). Although it can be forced out of the form with a Bomb, its speed and power can make this a difficult task. Additionally, in the GameCube versions, touching the Guardian in its puddle form was unusually deadly (60 units of damage on Hard mode). This was dropped to 40 units on Hypermode in the New Play Control! Metroid Prime 2: Dark Echoes and Metroid Prime Trilogy versions.
According to Mike Wikan, the difficulty level of the Spider and Boost Guardian battles was a last minute change, three days before Echoes went gold. Kensuke Tanabe, the game's producer, felt that the battles were not challenging enough and asked that they be made harder, but as a result they became extremely difficult. Both battles' difficulty levels were reduced for the Wii rereleases of Echoes. Wikan informed Tanabe that the development team of Trilogy was reducing the difficulty, and Tanabe conceded it was the right decision.
Bryan Walker, senior director of development at Retro Studios, claimed in an interview with IGN that he was never able to defeat the Boost Guardian without going into debug mode.  He subsequently admitted that this statement was made out of irritation with the fight, and he has been able to defeat the Guardian without enabling developer control.
- The Boost Guardian is physically identical to the Jump Guardian, the only other Guardian Ing to be fought in its natural state. Despite this, there are a few differences between the two:
- Although both creatures are weak against the Light Beam, the Boost Guardian cannot be burned to death.
- The Boost Guardian demonstrates its puddle form(s) much more often than (if at all) the Jump Guardian.
- The Boost Guardian takes massive damage (only while in solid form) from Power Bombs (via Sequence Breaking), whereas the Jump Guardian is completely immune.
- The Boost Guardian is the first Ing boss that Samus fights without any accessible Light Crystals or Beacons. Quadraxis is the second and the Emperor Ing is 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, though she is not related to the Ing.
- In the internal 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.
Boost Powered Inglet.
Boost Ball ability grants great speed to enemy. Lure it into destroying crystals in area; the energy within will damage the creature.
This Inglet has absorbed the power of the Boost Ball. It is capable of energizing its body and boost-blasting it toward its enemies as a weapon. The presence of the Boost Ball has made the Inglet nigh-invulnerable; only pure light energy can damage it now. Expose the creature to pure light to destroy it.
- ^ KIWI TALKZ - #105 - Mike Wikan Interview (Metroid Prime Trilogy, Game Design, Crunch, Booz Allen Hamilton etc.) September 6, 2021. Retrieved September 18, 2021. Heard starting at 11:07 https://www.youtube.com/watch?v=hlbeRLmfCHk
- ^ "This was the topic of a lot of discussion during and even after we shipped, but the boost ball guardian was brutal. I confess here and now that I was never able to beat it without going into debug mode." "A Space Bounty Hunter in Texas" IGN. August 28, 2009. Retrieved on October 4, 2021. https://www.ign.com/articles/2009/08/29/a-space-bounty-hunter-in-texas?page=6
- ^ Reilly, Reece. "#109 - Bryan Walker Interview (Metroid Prime Trilogy, Donkey Kong, Mario Kart 7, Project Management)" (starts at 10:07). KIWI TALKZ. October 2, 2021. Retrieved December 9, 2021.
|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|