Izzet (blue/red) decks are not known for the ability to ramp, so you'll be spending the first few turns setting up mana rocks for mana generation, leaving your defenses open
You can tap them to create a Disenchant, Braingeyser, Terroir, Shivan Dragon, Regrowth, or Black Lotus, and then you can cast it, but you have to pay the cost for it
The First Chapter Sapphire/Steel A Steadfast Strategy While Set 2s Tactical Teamwork Starter Deck offers a portion of Sapphires draw engine, this one offers the cards youll need to ramp your Inkwell
Although it is no where near the level of finisher as a Baneslayer it is much more reliable value and immediate tempo, the latter of which is especially important against the decks you are playing life gain against