The cost reduction applies only to generic mana in the total cost of noncreature spells you cast
As long as there's still a spot at the event you want to swap to, yes definitely
If you have multiples of Dragoons Lance and Red Mages Rapier (by far the most powerful of the equipment cards in terms of pressuring life totals early) and copies of Suplex or Slash of Light to force through those attacks, you can go all-in with finishers like Unexpected Request and Zidane, Tantalus Thief to steal games before the opponent gets going
Like any collectible trading card game, cards can be desirable for a number of reasons, from the appeal of the artwork to the rarity of their distribution
With an Ink cost of 3, 2 Strength, 3 Willpower and 1 Lore, Ursula doesnt look great at first glance
Amber ink being the home of cheap and weak little characters, perfect for being banished into the discard pile, means that it shouldnt be too long until youre able to play Chernabog, Evildoer