My favorite EDH deck, Omnath, Locus of Mana, runs Traverse the Outlands. Omnath receives +1/+1 for each green mana in my pool. Traverse the Outlands allows me to tutor out basic lands to the battlefield based on the greatest power among creatures I control.
My question is: when does Traverse the Outlands status check? For instance, if Omnath is my biggest creature at 6/6 (receiving the +5/+5 from 5 green mana), would Traverse the Outlands check the power as it is cast, reading Omnath as a 6/6, or as it revolves, reading Omnath as a 1/1?
Traverse the Outlands checks to see what the greatest power is among creatures you control as it is resolving.
So in your example it will see Omnath as just a 1/1.
Even if it did check on cast, a spell isn't cast until all of its costs are paid.
Rule 601: Casting Spells
[...]
601.2. To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect.
[...]
601.2h The player pays the total cost in any order. [...]
601.2i Once the steps described in 601.2a–h are completed, [...] then the spell becomes cast. [...]
My question is: when does Traverse the Outlands status check? For instance, if Omnath is my biggest creature at 6/6 (receiving the +5/+5 from 5 green mana), would Traverse the Outlands check the power as it is cast, reading Omnath as a 6/6, or as it revolves, reading Omnath as a 1/1?
So in your example it will see Omnath as just a 1/1.
Hope that helps.
Two Score, Minus Two or: A Stargate Tail
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[...]
601.2. To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect.
[...]
601.2h The player pays the total cost in any order. [...]
601.2i Once the steps described in 601.2a–h are completed, [...] then the spell becomes cast. [...]
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules