So in a Commander match a buddy threw down Helm of the Host and Ghired, Conclave Exile. He attached the equipment to his Commander and swung out. Given the cards' rules texts, what goes onto/off of the stack and does this interaction would result in an infinite combo?
This is not an infinite combo
Here are the relevant steps, in order:
- You enter combat, and Helm of the Host creates a token copy of Ghired. The token is not legendary, and has haste.
- The token entering the battlefield creates a 4/4 Rhino. (The Rhino does not have haste.)
- You declare attackers, attacking with both Ghireds
- Both Ghired populate triggers go on the stack
- The first trigger resolves, creating a copy of the Ghired1 token. The token is not legendary, but does not have haste2, and enters the battlefield tapped and attacking. The token enters the battlefield in the state of "having already attacked", and therefore the game does not 'see' the moment that it did attack (which would have been during the declare attackers step, which has already passed), and it does not trigger the populate effect.
- The game does, however, see it enter the battlefield, so you do get another Rhino token.
- Repeat steps 5 & 6 with the second populate trigger.
- You now have 4 Ghireds. One is the original card, one is the Helm token, and two are the populate tokens. All four are attacking. You also have 3 new rhino tokens (plus probably one from when the first Ghired entered the battlefield). These tokens are not attacking.
- Opponent declares blockers.
1 You could in theory populate the Rhino, but why would you want to?
2 This is due to how copy effects work. Copy effects only copy the "copiable values" of the permanent, which is generally the original text of the card as modified by copy effects themselves. All other affects (e.g. "target creature gains flying", "target creature gets +1/+1") are ignored. On Helm of the Host, the removal of the Legendary supertype is part of the copy effect, while Haste is granted afterwards. Therefore the lack of Legendary is copiable, but the Haste is not. This isn't particularly relevant, because haste only affects whether the token can be declared as an attacker, and entering the battlefield tapped and attacking skips this step (which is the same reason you don't get more tokens).
Incidentally, Magic tries to avoid permanently granting abilities through static effects, as this creates memory issues. But they sometimes make exceptions for haste on wordy cards, with the theory being that haste is only relevant for one turn anyways. But it's worth paying attention to if you're facing down a Gingerbrute or dealing with Control Magic.
No. Ghired does not go infinite with Helm of the Host. Whenever ~ attacks abilities trigger when those creatures are declared as attackers - You will be able to attack with the original Ghired and the token created by Helm of the Host, both of which will trigger populate, but the tokens that those populate abilities create will not have their abilities trigger.
Each turn you can more than double the number of Ghired creatures you have, and gain 4/4s from his enters the battlefield, but the populate abilities on those new tokens will not trigger. This is covered by rule 508.2a and 508.3a of the comprehensive rules (emphasis mine):
508.2a Abilities that trigger on a creature attacking trigger only at the point the creature is declared as an attacker. They will not trigger if a creature attacks and then that creature’s characteristics change to match the ability’s trigger condition.
508.3a An ability that reads “Whenever [a creature] attacks, . . .” triggers if that creature is declared as an attacker. Similarly, “Whenever [a creature] attacks [a player or planeswalker], . . .” triggers if that creature is declared as an attacker attacking that player or planeswalker. Such abilities won’t trigger if a creature is put onto the battlefield attacking.
It is also in the rulings for Ghired on gatherer (emphasis mine):
Although the token is an attacking creature, it was never declared as an attacking creature. This means that abilities that trigger whenever a creature attacks won’t trigger when it enters the battlefield attacking.
Since the tokens were not declared as an attacker, but forced in attacking, the populate does not trigger.
No, there is no infinite combo here.
Helm of the Host creates a non-legendary copy of Ghired just before you attack. Both Ghireds could create additional non-legendary Ghired tokens that are tapped and attacking, so on the first time you attack, you can get up to 3 non-legendary Ghired tokens plus the original.
However, these populate tokens do not trigger their own attack abilities, only the Helm token does. A creature that enters the battlefield already attacking has never actually been declared as an attacker because it has been created after the declare attackers step. Therefore it doesn't trigger any abilities that trigger on attack, which is necessary for the populate to happen.
The 5 steps of combat are:
Beginning of combat. This is where Helm triggers and resolves, and where you get 1 Ghired token
Declare attackers. This is where you can declare all existing Ghireds to attack and get that many populate triggers. The populate tokens enter the battlefield but are not declared as attackers because they're already attacking, so you don't get additional populate triggers
Combat damage (1 or 2)
End of combat
Effectively, you can create x+3 Ghired tokens per attack, where x is the number of Ghired tokens you already controlled before the Helm trigger. That will of course grow quickly, but not arbitrarily quickly.