Morophon, the Boundless
Legendary Creature — Shapeshifter
Changeling (This card is every creature type.)
As Morophon enters, choose a creature type.
Spells of the chosen type you cast cost 
less to cast. This effect reduces only the amount of colored mana you pay.
Other creatures you control of the chosen type get +1/+1.
Victor Adame Minguez
Rulings
If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. For example, if a spell of the chosen type costs {2}{W/U}{W/U}, you may choose for the cost to be {2}{W}{U} and then reduce it to {2}.
(wotc • 2019-06-14)
Morophon's effect reduces the total cost by up to one mana of each color. For example, if a spell of the chosen type costs {4}{R}{W}{W}, it will cost {4}{W} after applying Morophon's effect.
(wotc • 2019-06-14)
You must choose an existing creature type, such as Sliver or Warrior. Card types such as artifact, and supertypes such as legendary or snow, can't be chosen.
(wotc • 2019-06-14)
Cost reduction effects are applied after other cost modifiers, so Morophon can reduce additional costs or alternative costs of spells of the chosen type.
(wotc • 2019-06-14)
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to other creatures you control of the chosen type may become lethal if Morophon leaves the battlefield during that turn.
(wotc • 2019-06-14)
Rulings
If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. For example, if a spell of the chosen type costs {2}{W/U}{W/U}, you may choose for the cost to be {2}{W}{U} and then reduce it to {2}.
(wotc • 2019-06-14)
Morophon's effect reduces the total cost by up to one mana of each color. For example, if a spell of the chosen type costs {4}{R}{W}{W}, it will cost {4}{W} after applying Morophon's effect.
(wotc • 2019-06-14)
You must choose an existing creature type, such as Sliver or Warrior. Card types such as artifact, and supertypes such as legendary or snow, can't be chosen.
(wotc • 2019-06-14)
Cost reduction effects are applied after other cost modifiers, so Morophon can reduce additional costs or alternative costs of spells of the chosen type.
(wotc • 2019-06-14)
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to other creatures you control of the chosen type may become lethal if Morophon leaves the battlefield during that turn.
(wotc • 2019-06-14)