Draco
Artifact Creature — Dragon
Domain — This spell costs 
less to cast for each basic land type among lands you control.
Flying
Domain — At the beginning of your upkeep, sacrifice this creature unless you pay 
. This cost is reduced by for each basic land type among lands you control.
Sam Wood
Planeshift (PLS)
• #131Rulings
Domain abilities count the number of basic land types among lands you control, not how many lands you control or how many of any type.
(wotc • 2021-06-18)
The basic land types are Plains, Island, Swamp, Mountain, and Forest. Land types other than basic land types (such as Desert) don't contribute to domain abilities.
(wotc • 2021-06-18)
Rulings
Domain abilities count the number of basic land types among lands you control, not how many lands you control or how many of any type.
(wotc • 2021-06-18)
The basic land types are Plains, Island, Swamp, Mountain, and Forest. Land types other than basic land types (such as Desert) don't contribute to domain abilities.
(wotc • 2021-06-18)