Both green and black provide excellent sacrifice outlets to abuse with Reyhan, but youll want some cards that bring counters along too
You get to draw tons of cards, buff your creatures, gain life, and ramp two mana
Youll get extra cards when your equipped creatures attack, and even if they die attacking, you can transfer equipment to Nahiri to make a really menacing commander and win via commander damage
If youve got a small creature you prefer to be something else, it can do that, and if theres an opposing threat that cant be destroyed, it can deal with that too
So that was a natural thing
Discarding a shrine card is something youre only likely to do in Limited when you have duplicates you cant play, but even then you definitely prefer to discard lands