Tanana Tribal Elder and Mufasa Respected King make too many vanilla (no ability) cards at that 4-ink cost
Rikku, Resourceful Guardian allows you to force a creature through your opponents' blockers, as well as steal counters, and Lulu, Stern Guardian protects you by putting stun counters on your opponents creatures, as well as proliferating to keep them around
This means it does literally nothing at first, but can quickly scale to become incredibly dangerous in the right deck
If you have a lot of decks like that in your local playgroup, you can take advantage of the End the Turn part of Ultima to stop things happening after it resolves
So its no surprise that Robin Hood, Champion of Sherwood is relatively expensive even as a non-Enchanted card
Another great Amber combo revolves around Song actions