Adding mana equal to the number of anything gets out of control quickly, especially when anything is a card type that's notoriously hard to remove in multiples
It was a playset in Standard back in the day and it sees play in Voltron Commander decks too
Sahagin 1U Creature : Merfolk Warrior Whenever you cast a non-creature spell, if at least 4 mana was spent to cast it, put a +1/+1 counter on this creature and it cant be blocked this turn
Her ability triggers when any player loses life (you included), so you if you cast Norn's Annex by paying plus 4 life, she'll trigger her card-draw ability on your end step (on top of triggering her last ability when you cast it)
Why Amethyst Is Positioned to Dominate Early Fabled Meta Before diving into specific cards, let's talk about why Amethyst synergies are particularly strong right now
It should be useful in Limited