MScore: 10.0/10
Herald's Horn
Artifactuncommon
As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost 
less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.
Illustrated by Jason Felix · The List · #C17-53
Rulings for Herald's Horn
4
2017-08-25
If you somehow control a Herald's Horn with no chosen creature type, no spells will cost less to cast, not even creature spells with no creature type. You'll be able to look at the top card of your library at the beginning of each of your upkeeps, but you can never put it into your hand this way, even if it's a creature card with no creature type.
2017-08-25
The effect of Herald's Horn reduces only generic mana in a spell's cost. If that cost has no generic mana, the cost isn't reduced.
2017-08-25
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
2017-08-25
If you don't put the top card of your library into your hand, you put it back on top of your library without revealing it. You'll draw it in that turn's draw step.
: Look at the top three cards of your library. You may reveal a creature card of the chosen type from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
less to cast.
: Look at the top four cards of your library. You may reveal an artifact card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.