After years of guides assuring me that "the GameCube titles raise the catch rates of Shadow Pokemon to make them easier to catch!" I'd assumed that the catch rates of all the legendaries in Colosseum/XD were... actually significantly higher than they typically are in the main series. Never actually had cause to look it up but, while looking up the catch rate of something else on Bulbapedia's big list, my eye was caught by the little asterisk next to a couple of Pokemon indicating that an exception was made at some point and so it turns out that Suicune, Entei, and Raikou's shared catch rate of 3 was indeed raised in Colosseum... to 15.
Not 45 or 60 or even 75 or something a bit more generous like you'd expect. 15.
Meanwhile the sequel was a bit more forgiving with Articuno, Zapdos, and Moltres - they got their catch rate of 3 raised to 25 instead. Lugia's rate is unchanged, which I suppose is because you're expected to just use the Master Ball on it (and honestly why wouldn't you)
In fact, the idea that most Pokemon in those games got a catch rate increase is largely only true in XD, which makes a lot of its lategame Pokemon easier to catch - Snorlax and Chansey went from 25 and 30 respectively to 70; a bunch of base-45s like Kangaskhan, Tangela, Swellow, Manectric, and Altaria got generously boosted to 80 or 90; it pushes some species like Starmie, Magcargo, and Marowak from 60/70 to over 100; and even a couple of species like Primeape and Hypno get extremely small boosts you'd hardly notice too because hey why not. It also brings Houndour up to the same general catch rate as the other Pokemon it's caught alongside (Spheal, Seedot, Hoothoot, Gulpin, and Mareep).
Turns out, minor increases for legendaries aside, Colosseum actually makes several of its species harder to catch! Metagross gets the same increase as the beast trio - 3 to 15 - and most evolved/late-game species like Hitmontop, Mantine, Heracross, Ursaring, Houndoom, and Forretress were left unchanged, but it tweaks the rates of several other Pokemon, including Skarmory (which goes from 25 to 15), Togetic (75 to 45), and the unexpected big winner/loser* Tropius (200 to 45 - by far the biggest change). While Tyranitar, which had an initial catch rate of 45, gets reduced to just 10. The Pokemon significantly improved are the Johto starter trio, who all get their rates raised from 45 to a rather generous 180.
God, they really wanted to make Colosseum as hard as they possibly could, didn't they? I kind of dig it and I'm finding it really funny I've played that game several times always thinking the catch rates for all the Shadow Pokemon were uniformly better than the main series. except I quite often used the Master Ball glitch and so, even more amusingly, all the lowered catch rates were never an issue, oh well never mind hard luck Genius Sonority you tried your best
*depending on your outlook