Eliza Hawkins, Runaway Scholar

When Eliza enters the battlefield, create Mystrin,
a legendary 1/1 blue Bird creature token with
flying.
{u}{u}{b}: Target player reveals their hand. You
choose an instant or sorcery from among the
revealed cards and exile it. As long as Eliza
Hawkins remains on the battlefield, you may
cast cards exiled this way, and you may spend
mana as though it were mana of any color to
cast those spells.