First off every 5 million exp past 100th a dragon would go up a rating point(solving some powerlevelling and grouping issues).
The exp could be spent on various abilities and stats and you obviously could not get everything. This would lead to each dragon being somewhat different // customized (which is a very good thing).
You could spend exp on the following abilities:
Base Strength (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Dexterity (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Power (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Focus (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Health (10 points) -> 2 million exp (repeatable, +10% cost per time taken)
Base Armor (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Evasion (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Tooth/Claw (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Base Primal (10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Etheral Armor (10 points) -> 7 million exp (repeatable, +10% cost per time taken)
Dragon Breath(10 points) -> 5 million exp (repeatable, +10% cost per time taken)
Dragons Gift V -> 20 million exp (one time only)
Refreshing Breeze timer reduction(10 seconds) -> 5 million exp(doable 6 times, +20% cost per time taken)
Tail Whip Stun Duration Increase(1 second) -> 5 million exp(doable 5 times, +20% cost per time taken)
Stunning Bolts(2% chance for a bolt spell to stun target 5 seconds) -> 5 million exp(doable 5 times, +20% cost per time taken)
Critical Heals(2% chance for a heal/hot tick to heal double) -> 5 million exp(doable 5 times, +20% cost per time taken)
Penetrating Winds(+25 accuracy with grazing/unrelenting winds) -> 5 million exp(doable 5 times, +20% cost per time taken)
Golden Bolt(shares timer with gold rage -- fires a triple bolt at target, shares gold rage timer) -> 20 million exp(one time only)
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Example of the costs:
First time you take refreshing breeze reduction it costs 5 million exp
The second time it takes 20% more -- 6 million exp
Third time 20% more - 7.2 million exp
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Obviously there are other things that could be added to this idea but this is the gist of a potential way dragons could be allowed to advance post 100 and hence give them something to do with exp, significantly reduce the powerlevelling problems out there, and allow dragons to better group with bipeds.