My reaction was it does not change the outcome, because the -1/-1 was not placed on that creature, then it entered the battlefield. So my question is, are those "each creature" mods state based so it would be on ALL creatures until end of turn, or is it just on the creatures that are on the battlefield at that moment.
They can't cast Cower in Fear before Hamletback Goliath is cast. It is already cast in that situation (since they are responding to it). Also, if they cast Cower before the Goliath resolves, it won't do anything. I think you mean to say they cast it after Goliath resolved but before the Surge trigger resolved (since the Warstorm Surge won't rigger until Goliath is already on the battlefield after resolving).
So, here is what happens:
Hamletback Goliath is cast. Priority passes and no one does anything.
Goliath resolves.
When Goliath enters the battlefield, Surge triggers and a target is chosen.
In response to the trigger, the opponent casts Cower.
Priority passes and Cower resolves. Goliath is now a 5/5.
Surge trigger resolves and will cause the Goliath to deal damage equal to its power to its target. Its power is 5 so it will deal 5 damage to the 6/6.
The 6/6 will have 5 damage marked on it and will survive.
Warstorm Surge cares about the power of the creature when the trigger resolves (or as it last existed on the battlefield if it dies before the trigger resolves). Power and Toughness increases and decreases are taken into account. It doesn't matter that the -1/-1 wasn't "placed" on the Goliath. It was on the battlefield when Cower resolved so it is affected.
I could be misunderstanding the order things actually happened, but in your scenario this is a legal play as long as everyone does everything at the right time (see my summary above). In a casual setting it seems obvious what the intent is so I would say that you should move forward with that intent and just make sure everyone knows the appropriate steps for doing what they want.
Thank you, that clears up a lot. I am still confused whether a mod would be on a creature if it enter the battlefield after an "each creature" mod resolves if the card applying the mod is a sorcery or instant.
"Mod" isn't a term used in Magic. In this case, it is a Continuous Effect. And no. If a creature enters the battlefield after a Continuous Effect has been created that modifies the power and/or toughness of creatures on the battlefield, it will not be affected by that Effect.
So, in the original example, if a Raging Goblin were cast after Cower resolved, it would just be a 1/1. It won't get -1/-1 from Cower.
You are right cower in fear would resolve then hamletback would enter the battlefield as a 6/6. what the opponent would need to do in order to weaken the damage would be to cast cower in fear in response to warstorm surge triggering, so hamlet would enter as a 6/6 then warstorm would trigger, then cast cower in fear, to reduce it to 5/5 then warstorm would only do 5 damage.
I am still confused whether a mod would be on a creature if it enter the battlefield after an "each creature" mod resolves if the card applying the mod is a sorcery or instant.
Only effects created by static abilities (rule 112.3) will affect those creatures that enter the field on a later time. (rule 611.3)
All other sources of effect will only affect those creatures which are on the field here and now, not affecting future creatures, the only exception being those effects which change the rules of the game. (rule 611.2c)
Thank you for any help.
So, here is what happens:
Goliath resolves.
When Goliath enters the battlefield, Surge triggers and a target is chosen.
In response to the trigger, the opponent casts Cower.
Priority passes and Cower resolves. Goliath is now a 5/5.
Surge trigger resolves and will cause the Goliath to deal damage equal to its power to its target. Its power is 5 so it will deal 5 damage to the 6/6.
The 6/6 will have 5 damage marked on it and will survive.
Warstorm Surge cares about the power of the creature when the trigger resolves (or as it last existed on the battlefield if it dies before the trigger resolves). Power and Toughness increases and decreases are taken into account. It doesn't matter that the -1/-1 wasn't "placed" on the Goliath. It was on the battlefield when Cower resolved so it is affected.
I could be misunderstanding the order things actually happened, but in your scenario this is a legal play as long as everyone does everything at the right time (see my summary above). In a casual setting it seems obvious what the intent is so I would say that you should move forward with that intent and just make sure everyone knows the appropriate steps for doing what they want.
So, in the original example, if a Raging Goblin were cast after Cower resolved, it would just be a 1/1. It won't get -1/-1 from Cower.
.
All other sources of effect will only affect those creatures which are on the field here and now, not affecting future creatures, the only exception being those effects which change the rules of the game. (rule 611.2c)
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules