I would suggest cutting most of the always enter tapped lands you have for basics (or even previously suggested lands) as discard tribal loses a lot of it's strength the longer the game goes on and players run out of cards in hand, always enters tapped lands hurt tempo making the deck slower.

Now that being said flavor wise Crosis, the Purger maybe the stronger "specter" elder dragon, course bolas is stronger overall, but maybe let crosis join the party in the 99?

If you are looking for more / better specter cards, there are some that are not technically specter's but still have the discard effect such as Kheru Mind-Eater , Dreamstealer , Liliana's Reaver .

You can also double the triggers with Strionic Resonator , Fireshrieker , and Grappling Hook .

And as long as you are getting in for combat damage, why not run Sword of the Animist , Bloodforged Battleaxe, Mask of Memory , or even Quietus Spike / Scytheclaw ?

Also, Rogue's Passage is a pretty decent land if you can't get in easily.

Finally, Sepulchral Primordial can get some value from those discarded cards.