Manahive

Here are some cards equivalent to Tamiyo, Inquisitive Student (blue, low-cost, transform into a planeswalker):
1. Delver of Secrets (one-mana blue, transforms into a stronger creature)
2. Thing in the Ice (two-mana blue, transforms based on spells cast, powerful effect)
3. Jace, Vryn's Prodigy (two-mana blue, transforms into a planeswalker)

Reason: All are blue, low mana, enter as creatures and transform based on in-game triggers.