Scion of Draco
Artifact Creature — Dragon
Domain — This spell costs 
less to cast for each basic land type among lands you control.
Flying
Each creature you control has [[ keyword: "vigilance" ]] if it's white, hexproof if it's blue, [[ keyword: "lifelink" ]] if it's black, first strike if it's red, and [[ keyword: "trample" ]] if it's green.
Greg Staples
Modern Horizons 2 (MH2)
• #234Rulings
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)
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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)