Pokemon Colosseum beaten. The final boss was really scary due to level creep, being ~5 levels above the penultimate boss who in turn had ~5 more than the preceeding enemies. His Slaking could OHKO Raikou with Crush Claw after an X Attack while not taking significant damage from anything I could throw it. Thankfully the AI is kinda dumb so his ally Machamp finished him off with Earthquake before the Skill Swap Slowking could come out, which would've been REALLY scary. Rest of the team (Scizor, Salamence, Dusclops) was not exactly chopped liver, either.
Colosseum story mode's short length and weird level curve make it feel more like an experiment or test run than a proper RPG. You start with an L26 Umbreon and L25 Espeon, the snagable Shadow Pokemon start at L30 with all three stage Pokemon starting at tier 2 (and even some two stage lines), while the main game ends around L48-50 (depending on how many optional battles you go for) - it all kinda feels like you skip the first half of a normal-lengthed game. The high starting levels and lack of a move relearner also mean that moves you'd normal take for granted in other games are impossible to get in Colosseum, like Leech Seed on Jumpluff.
The double battle emphasis and catching Pokemon during boss battles are novel twists on the usual Pokemon format, albeit ones that XD later refined into a much better RPG. Colosseum's most enduring novelty is that the playable roster consists about 90% of gen 2 Pokemon, with just a few gen 3 mons mixed in. This is a welcome change from Johto, where gen 2 Pokemon are often obscured and largely overshadowed by their gen 1 counterparts. Oh, and there's an infinite Pokeball glitch that's pretty hilarious in practice.
Some thoughts on the Pokemon I ended up using:
Espeon: Irreplacable earlygame MVP, as I mentioned previously. Low physical durability gradually became a problem later on, but the offense was still priceless, getting more turn 1 OHKOs than anyone else by far. The lack of an Alakazam (or any other Psychic, save Meditite) makes the late Psybeam/Psychic pickups sting less in this game.
Jumpluff: The lack of Leech Seed and Stun Spore really suck, but it's both the fastest and most accurate sleep move in the game by a significant margin, not counting Yawn users, especially in a game where every single catchable Pokemon has a non-typed recoil move to potentially suicide with. The completionist in me wanted to snag every Shadow Pokemon to make things more interesting, so Jumpluff was a must.
Quagsire: Water and Ground are priceless types for the story Mt. Battle sequence, while Shadow Pokemon lab was filled with Rain Dance+Thunder spamming Electrics that come before the Earthquake TM. Quagsire thus filled valuable type niches before ultimately being phased out after I caught Water and Ground types with significantly better stats.
Suicune+Raikou: Rain Dance+Surf+Thunder ahoy. Gen 3 Surf doesn't hit allies but only does half damage to each target, so the damage boost from Rain Dance matters more than in singles-based RPG. Raikou's speed makes it ideal for Thunderdancing, which is good because its movepool is pretty barren otherwise. Suicune's Aurora Beam is valuable in a game where Ice Beam TMs are hard to get, and the durabilities on both mattered a lot since it's harder to play type advantages perfectly in an all-doubles game.
Flygon: Starting as a L43 Vibrava means you skip almost the entire painful NFE phase for this evo line for once, plus you get the Earthquake TM almost immediatly afterwards. It's pretty clearly the best Ground type in Colosseum (alternatives: Quagsire, Gligar, Piloswine) which helps its case for that TM, in an all-doubles game where Earthquake naturally dominates. Luckily Protect is storebought, so I gave it to Espeon/Suicune/Raikou so Flygon could safely use EQ with any partner out. Crunch/Dragonbreath/storebought Fire Blast gave it some respectable options for Ground resists/immunes.
Skarmory: Last minute filler addition, mainly to get a Ground-immune with better damage/durability than Jumpluff for battles where I want Flygon to use EQ more than just every alternating turn.
My copy of Alpha Sapphire's supposed to arrive tomorrow, so I'm done with the game for the time being. Colosseum's postgame doesn't sound all that interesting on paper, so who knows if/when I go back and pick it up.