I have a Nacatl War-Pride in play. I cast Gigantiform on it during my pre-combat main phase, and attack. Ordinarily, the Nacatl tokens wouldn't get any buffs off an enchantment, but I think that because Gigantiform modifies its base power/toughness, it would still apply. My best guess is that the tokens would be 8/8 creatures, but they wouldn't have trample. Am I correct?
When a card like that says to copy it, it copies it's printed values of the card, not any modifications to it.
The only exception being if the copied card is also a copy of something. Cloning a Clone which has cloned another creature will give you another of that creature, not a 0/0. However, in this case they are just normal 3/3s.
To the edit: the original War-Pride is attacking alone if you don't declare any other attackers, at least for long enough for exalted, etc to trigger.
Well, assuming the War-Pride was the only creature to be declared as an attacker, it would receive any Exalted bonuses. Exalted checks the number of creatures that were declared as attackers, not the number of creatures attacking. Since the tokens are directly put onto the battlefield tapped and attacking (and therefore weren't DECLARED as attackers), they won't affect whether or not Exalted bonuses are given.
The problem with defining this format by what is "fun" is that everyone seems to define fun as what they don't lose to. If you keep losing to easily answered cards, that means you should improve your deck. If you don't want to improve your deck, then you should come to peace with the idea that you are going to lose because you chose to not interact with better strategies.
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How would it interact with any exalted bonus? Sovereigns of Lost Alara?
The only exception being if the copied card is also a copy of something. Cloning a Clone which has cloned another creature will give you another of that creature, not a 0/0. However, in this case they are just normal 3/3s.
To the edit: the original War-Pride is attacking alone if you don't declare any other attackers, at least for long enough for exalted, etc to trigger.
Are all of the tokens exiled on the same trigger, which would make it able to be stifled?
Yes