Radha's Firebrand
Creature — Human Warrior
Whenever this creature attacks, target creature defending player controls with power less than this creature's power can't block this turn.
Domain — 
: This creature gets +2/+2 until end of turn. This ability costs less to activate for each basic land type among lands you control. Activate only once each turn.
Ângelo Bortolini
Dominaria United (DMU)
• #408Rulings
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 • 2022-09-09)
Increasing the target creature's power in response to Radha's Firebrand's first ability can cause it to be an illegal target for the ability. However, once the ability has resolved, it won't be able to block even if its power becomes greater than Radha's Firebrand's power.
(wotc • 2022-09-09)
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 • 2022-09-09)
Related Cards
Printings
Rulings
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 • 2022-09-09)
Increasing the target creature's power in response to Radha's Firebrand's first ability can cause it to be an illegal target for the ability. However, once the ability has resolved, it won't be able to block even if its power becomes greater than Radha's Firebrand's power.
(wotc • 2022-09-09)
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 • 2022-09-09)