The cost reduction applies only to generic mana in the total cost of blue spells you cast
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owners control with a -1/-1 counter on it.) Illustrated by Karl Kopinski Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Legal Brawl Not Legal Legacy Legal Comp
On top of it, if you deal combat damage to the opponent, you can look at the top of your library and summon Dinosaur creatures revealed onto the battlefield allowing you to create a wide board which might prove to be to difficult for your opponent to deal with
One of the most underrated aspects of card design today is the shift from rares that are bad 100% of the time to rares that are bad 99% of the time but are totally awesome in very specific circumstances
Narset of the Ancient Way is probably the best option: while she incentivizes casting spells over cycling them, her minus ability allows you to draw extra cards with the option to discard them to damage your opponents creatures, or to keep them and cycle them later
As always, I'm very eager to hear your thoughts on today's column and Throne of Eldraine in general