The point of this monster is to be a variety of dragon that truly could be a frightening threat against a party of 5 PCs. I have used some of the suggestions made by the great folks at Radio Free Hommlet, Sly Flourish and the Chatty DM.
Here are some of the alterations I have made to the Elder Blue Dragon to come up with the new version.
1. The defenses and hit points have been reduced to what would be expected for a Level 20 monster, as recommended from Monster Manual 2.
2. The dragon now has an aura which allows it to shoot a bolt of lightning at it's oppenent at the beginning of it's opponent's turn. This allows the encounter to scale according to party size, and also substantially increases the amount of attacks it can make.
3. Damage types have been altered, adding thunder to the lightning damage for the breath weapon, and making the damage from the claws and gore untyped. This will make it a threat to parties that have good resistances to lightning.
4. The Blue Dragon is a bit different from other dragons in that it's breath weapon was an at-will. However, I switched it back to a Recharge 5 but also dramatically increased the damage that it puts out. Largely this was done because of the existence of another at-will 'breath weapon' which is an Area Burst attack.
5. Since it's important for the dragon to be able to fly around sniping the party, it's critical that it has the capability to get away from Defenders and other powers that might permanently ground it for the duration of the battle. The Take to the Air power allows this, and combined with the already existing Thunderclap power, the dragon has at least the ability to do this. I did however, reduce the stunned effects in the Thunderclap power to Dazes, for player enjoyment.
6. The dragon now gets a minor action, that doesn't do any damage, but it does give a minor control ability.
7. The dragon now gets substantially stronger damage-wise when it's bloodied, but it also gets easier to hit, reducing 'grind' effects.
8. Stuns and dazes only eliminate the standard action now, which does substantially hamper the dragon, but doesn't completely neuter it either.
It does have a fairly large stat block, but it is designed to be truly encountered alone, with the possible exception of hazards, traps or environmental effects.
So what do you think?