Entei
Availability: Mt. Battle via Admin Dakim at Level 40, or Realgam Tower or even Under Colosseum in the postgame. A point directly after you get to purify your Pokemon.
Heart Gauge: 13,000
Overview: Of the four Fire-types in the entire game, Entei stands out from the others due to being a Legendary. With a high BST, great offenses, very solid defenses, and one of the fastest Pokemon you can catch, it holds up well, even against Earthquake spam. With a base 115 attack stat, Entei has one of the hardest hitting Shadow Rush in the game. It gets Sunny Day when its purified so its Fire Blast becomes one of the hardest hitting moves in the entire game even though it only comes off of a base 90 sp. attack. Entei is held back by its awkward movepool having to rely on its weaker offensive stat in most situations. Even with the oddities in its movepool, it still can power through most encounters fairly easily due to its overwhelming stats. Fire in general is a great offensive typing to have for the major battles.
Additional Notes: Entei makes for a top Time Flute candidate due to its large Heart Gauge, but it also makes for a great Shadow Pokemon as Hyper Mode Shadow Rushes hit extremely hard. Entei can also make great use of the TM Return, from which you can obtain from Justy. Interestingly enough, the Beasts have a somewhat higher capture rate due to the fact that the Pokeball always shakes at least once. As Entei is a Legendary, it is also part of the Slow experience group.
Flaaffy
Availability: Pyrite Town via St. Performer Diogo. Found early game at level 30. Optional battle.
Heart Gauge: 3000
Overview: Flaaffy has a weird time as a Shadow Pokemon. It has to mostly rely on Shadow Rush, running off of a base 55 attack but as it comes further along, it relearns moves like Thunder Wave and Cotton Spore, which give it great utility in crippling Pokemon as well as capturing other Shadow Pokemon. Once it's purified, it gets the much more powerful Thunderbolt to use and when it evolves into Ampharos, it gets a big boost in power and defenses. Its offensive movepool, like most Electric types, lacks on the special side but can mostly get the job done with Thunderbolt due to its high base 115 special attack. Flaaffy/Ampharos tends to struggle in the early due to a slow base 55 speed, the huge amount of ground types seen as well as the lack of power needed, but starts to excel after that as ground types become increasingly rare and gains further utility moves such as Light Screen.
Additional Notes: Ampharos does have a decent physical movepool if one really needs to rely on it, but those moves are better off taught to physically stronger Pokemon. Ampharos is best paired with a Pokemon that can handle ground types, like Feraligatr or Suicune for example.
Makuhita
Availability: Phenac City via Miror B. Peon Trudley at level 30, or postgame in the same area.
Heart Gauge: 3000
Overview: Makuhita has some pretty rubbish stats with its only base stat being above 70 is its HP and struggles in the early game, where it will spend a lot of its time getting OHKO'd, but once you're able to purify it, if you raise it at least one level, it will evolve into Hariyama it gets a massive increase in all of its stats, except for speed. A beefy base 144 HP stat allows it to take hits, and a great base 120 attack lets it dish them out. A great Fighting STAB and two great abilities in Guts or Thick Fat lets Makuhita/Hariyama become a solid and sturdy tank. Hariyama is a bit reliant on TMs if it wants coverage, but hits hard enough that it's not necessary to have.
Additional Comments: Since Makuhita is the tutorial Mon, it also has a 100% capture rate so you can just simply chuck a Pokeball at it. You can opt to beat the Pyrite Colosseum a few times to nab the TMs for Focus Punch and Brick Break if you don't want to deal with Cross Chops low PP and funky accuracy. Vital Throw does have situational use, as it has perfect accuracy and there are many Pokemon that like to abuse moves such as Double Team and Sand Attack.
Quagsire
Availability: Pyrite Town via Bandana Guy Divel. Found early game at level 30. Optional battle.
Heart Gauge: 4000
Overview: Quagsire makes its mark by being one of the few fully evolved Pokemon one will have for the first quarter of the game. With a base 85 attack, it has a strong Shadow Rush when its obtained and also has a good 95/85/65 bulk. Water/Ground is also a good offensive and defensive typing having only one weakness and hitting 6 types super effectively. Quagsire also has the choice of either Water Absorb or Damp. Damp does have its occasional usage such as stopping a few Explosion using Pokemon, but Water Absorb is the more useful ability due to having way more chances to proc. Quagsire also has a great offensive movepool with Fighting, Steel, and Ice, a good support movepool such as Yawn, and Amnesia, and also naturally learns Earthquake. Even though Surf is missing as an HM, Quagsire is one of the few users of the move. It has a lowish base 65 base special attack and combined with Surf's double battle properties, Quagsire misses out on quite a few OHKO's it would normally get in the mainline games. Quagsire does have some issues in the early game with the common usage of grass types and being slow, and especially has a pretty awful performance against Miror B, but after that has a good showing in all other major battles.
Additional Notes: Yawn during certain major battles can force the AI to switch as they don't want the Yawn to proc the Sleep status. One can abuse this AI oversight to completely immobilize one side of the opponent if used correctly. Since Surf is considered an HM in the game, it has to be removed by the Move Deleter.
Quilava
Availability: Phenac City via Cipher Peon Rosso. Potentially found early game at level 30. Can also be found at Realgam Tower, or in the postgame at Snagem Hideout/Shadow Pokemon Lab if Bayleef/Croconaw are chosen.
Heart Gauge: 3000
Overview: Quilava is potentially the second shadow Pokemon you can obtain. The moves it comes with are Smokescreen, Dig and Flame Wheel, while obtaining Sunny Day when its completely purified. Quilava struggles during the early game because it has unfavorable matchups against the early game bosses but it does get a well rounded movepool consisting of fighting, ground, as well as its STAB. When it evolves into Typhlosion, its best quailty is its base 100 speed, tied for fourth place for the fastest Pokemon you can obtain. In the end it being fast, having good coverage, even though its fairly TM reliant, and a high base 104 sp. attack makes it a solid overall choice
Additional notes: Since Quilava does take the longest to evolve, being level 36, there is a good chance Quilava might still be a Quilava when the Dakim fight appears its head. It's in Typhlosion's best interest to be taught Fire Blast, as Flame Wheel is fairly weak, and it doesn't naturally learn Flamethrower until level 60.
Raikou
Availability: Shadow Pokemon Lab via Cipher Admin Ein. Found late game at level 40. Can also be found at Realgam Tower or postgame in the Deep Colosseum.
Heart Gauge: 13,000
Overview: Raikou, like its brethern, have some great stats. It hits hard on the special side, and its very fast too. It also has impressive 90/100 special bulk, but is a bit weaker on the physical defense. Like most Electric types, its special movepool tends to lack, but it has a respectable 85 base attack if you really need to use physical attacks on it. In Colosseum, Raikou is one of the three only Electric types in the game and even though Raikou and Ampharos have the same base special attack, Raikou trades paralysis utility for more bulk and a much higher speed stat. Raikou's role in most battles will be to set up Rain Dance and proceed to spam hard hitting Thunders. In the battles that Raikou can take part in, there are quite a few EQ users so one must be wary when using Raikou, but Raikou can learn Reflect to mitigate some of that damage. It's late encounter and low caught level are what mostly hurt Raikou, but if taken the time, Raikou can prove to be a valuable asset for the remaining battles.
Additional Notes: Arguably, Raikou makes the best candidate for the Time Flute due to how late it is caught compared to Entei and Suicune, and the Rain Dance+Thunder combo is hard to pass up compared to its decent Shadow Rush considering the attack power and level difference at that point in the game. Interestingly enough, the Beasts have a somewhat higher capture rate due to the fact that the Pokeball always shakes at least once. As Raikou is a Legendary, it is also part of the Slow experience group.
Suicune
Availability: The Under via Cipher Admin Venus. Found mid game at level 40. Can also be caught at Realgam Tower or postgame at Deep Colosseum.
Heart Gauge: 13,000
Overview: Suicune is the epitome of a tank. It is extremely bulky with 100/115/115 defenses, while also sporting a decent 90 Special Attack to deal back decent damage. It comes with the highly coveted Surf for strong STAB and also learns Aurora Beam one level after purification. Even though Suicune is very bulky, its support movepool lacks in some areas; it doesn't learn much moves that can hinder the opposing side, rather having moves that can support its partner such as Rain Dance, Reflect, and Mist. It does also struggle in some parts, like the Shadow Pokemon Lab where there are a ton of Electric-types to run into. Even with its faults, Suicune makes for a fine member and still ends up being one of the strongest Pokemon obtainable.
Additional Notes: Suicune is a high priority Time Flute user, with a second Time Flute being found within the area it's caught, though it does take a bit of exploring in the Subway to get since one needs the U-Disk to even get to the area. Because of its bulk, Suicune makes one of the best users of the Toxic TM. Suicune pairs best with other water types or Pokemon that can learn Thunder. Interestingly enough, the Beasts have a somewhat higher capture rate due to the fact that the Pokeball always shakes at least once. As Suicune is a Legendary, it is also part of the Slow experience group.
Umbreon
Availability: Starter (Level 26)
Heart Gauge: N/A
Overview: With 95/110/130 defenses, Umbreon is one of the bulkiest Pokémon in the game, being able to shrug off any neutral hit, and able to tank even the most powerful of super effective hits. The bulk comes in handy when trying to capture the Shadows and the low offenses also are very useful for that too, but the lack in power is very noticeable in major battles where Pokemon are beefier and hit harder and can lead to KO's on your side of the field. Umbreon makes a great support Pokemon due to a variety of utility moves such as Confuse Ray, Screech, Snatch, Taunt, and the only Pokemon in the game with Secret Power, which mostly acts like Body Slam in Colosseum due to Colosseum's terrain. Confuse Ray and Taunt are especially notable as many major battles tend to rely on status moves to utilize their strategies. Just like Espeon, it comes with Synchronize, but Umbreon takes on status conditions generally better.
Additional Notes: Opposite to Espeon, the AI tends to avoid double targeting Umbreon unless they can get multiple super effective hits on it. This does let Umbreon last even longer on the field and spread around status debuffs or stack on the damage, but one must take this into consideration when it is on the field as it can lead to an untimely demise of the other teammate.
Vibrava
Availability: Shadow Pokemon Lab via Cipher Peon Remil. Found late game at level 43. Can also be found in the same area in postgame.
Heart Gauge: 6000
Overview: Frankly, Vibrava sucks. Being frail, weak, and the moves it comes with leave much to be desired, but Vibrava is commonly held in a positive light in Colosseum. A Ground/Dragon typing with Levitate gives it a nice selection of resists and immunities, and the reason why its praised is for what it becomes, not it starts out as. When Vibrava becomes a Flygon, which is only two levels from when it is caught, it gets a big boost in all of its stats. That 50/50/50 "bulk" becomes 80/80/80 which lets it take quite a few hits with it's valuable dual typing. It now has a good base 100 attack and speed letting it hit hard, and fast consisting of coverage that includes its dual STAB, Fire, Steel, Dark, and Grass. Even with Flygon has great offensive pressure, but is very TM reliant for offensive presence, and has a nasty x4 weakness to Ice, which is fairly common to come across in the later major battles.
Additional notes: Because of how useful Flygon is, and how trashy Vibrava is, Vibrava makes one of the best candidates for the Time Flute. If one happened to save those Rare Candies from The Under, Vibrava also makes a good choice to use two of them if one immediately decides to purify it with the Time Flute. The TM for Earthquake also comes right after Ein, and Flygon is arguably the best user of Earthquake due to its speed, power and gaining STAB for it.
Vibrava oddly enough has a very long confusion animation so if one does use it for battles, try to avoid opponents with confuse ray/supersonic.