Dratini/Dragonair/Dragonite

The victor thrice, approacheth hence,
The door hath been blocked without sense.

At the Elite Four, to become the Champion, you must beat all four elites; after defeating three, the apparent final one approaches, and victory seems close at hand. The previously locked doors open as you defeat each elite.

Façade awaits you, keyholder,
Beware thy future batt’ling err;
Seek wisdom now, or fate is doom.

In RBY, after beating Lance, you are supposed to be the Champion. However, your rival has already beaten you to it, and in order to become Champion, you must defeat him in an unexpected battle. If you didn't bother to potion up and revive pokémon used against Lance because you thought you'd already won, you might be in trouble against your rival.

Light sheds as growth avoids its bloom.

Lance in RBY has Gyarados, Dragonair, Aerodactyl, and Dragonite. Dragonair is apparently able to control the weather according to the pokédex; its growth avoids its bloom because it is not fully evolved into Dragonite. Light sheds due to Dragonair's mastery over the weather.