Kinjalli's Caller
Oracle Text
Dinosaur spells you cast cost
less to cast.Card Rulings
9/29/2017 To determine the total cost of a Dinosaur spell, start with the mana cost or alternative cost you’re paying, add any cost increases, then apply any cost reductions. The converted mana cost of the creature remains unchanged, no matter what the total cost to cast it was.
1/19/2018 If an effect refers to a “[subtype] spell” or “[subtype] card,” it refers only to a spell or card that has that subtype. For example, March of the Drowned is a card that benefits Pirates and features Pirates in its illustration, but it isn’t a Pirate card.
I think it's quite easy having Inspiring Vantage, Rootbound crag and even Unclaimed territory or Aether Hub in standard.
While there are two 2-drops that help accelerate dinosaurs, there are almost no worthwhile 4-drop dinosaurs (of those revealed so far). With this card, you can accelerate into a 5-drop dino on turn 3.