You add just two counters on your blue planeswalker, because Doubling Season specifically says you only get double counters from an effect , and adding loyalty counters to activate a loyalty ability is a cost , not an effect
The chase cards from this set are Imperial Seal (one of the best black tutor cards of all time) at over $1,000, Ravages of War (a renamed Armageddon) at over $600 and Zodiac Dragon at $525
Lets take a look at three of the best
Skullclamp Skullclamp gives a creature +1/-1 and draws you two cards when that creature dies
Of course, if you are going to be playing Commander with opponents who are also using the LOTR set to build their deck, youre most likely to come up against one of the below cards as Commanders
Aurelia continues to be a viable combo Commander, and she combos with an increasing number of cards