Rulings

• 2006-09-25
  The affected creatures and the power/toughness bonus are fixed when Tromp the Domains resolves.
• 2006-09-25
  The effect counts basic land *types*, not the number of basic lands. Therefore the maximum bonus is +5/+5.
• 2006-09-25
  The creatures get trample once; they don’t get trample for each basic land type.
• 2009-02-01
  A number of nonbasic lands have basic land types. Domain abilities don’t count the number of lands you control — they count the number of basic land types among lands you control, even if that means checking the same land twice. For example, if you control a Tundra, an Overgrown Tomb, and a Madblind Mountain, you’ll have a Plains, Island, Swamp, Mountain, and Forest among the lands you control. Your domain abilities will be maxed out.
• 2009-02-01
  How many lands you control of a particular basic land type is irrelevant to a domain ability, as long as that number is greater than zero. As far as domain is concerned, ten Forests is the same as one Forest.
• 2009-02-01
  To determine the number of basic land types among lands you control, look at the lands you have on the battlefield and ask yourself whether the subtypes Plains, Island, Swamp, Mountain, and Forest appear within that group. The number of times you say yes (topping out at five) tells you how powerful your domain abilities will be.
• 2021-03-19
  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.
• 2021-03-19
  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.
• 2021-03-19
  The size of the bonus is determined only as Tromp the Domains resolves. Once that happens, the bonus won’t change later in the turn even if the number of basic land types among lands you control changes.
• 2021-03-19
  Tromp the Domains affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t gain trample or get a power and toughness boost.