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Describe the Bug:
AI equipped Argothian Pixies with Kitesail and so they got flying then I pinged them with Grapeshot Catapult's ability and Argothian Pixies was dealt 1 damage and died.
edit: Tested more and same happens with combat damage from Artifact creatures.
Which card did behave improperly?
Argothian Pixies.

Which update are you using? (date, name)Which type? (duel, gauntlet, sealed deck)
Manalink 2016/08/27: Eldritch Moon v2, duel

What exactly should be the correct behavior/interaction?
Argothian Pixies prevents all damage made to it by artifact creatures.

Are any other cards possibly affected by this bug?
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Fixed this & Argothian Treefolk in commit 46e264c

Now Argothian Pixies prevents all damage to itself from all artifacts (tested with Rod of Ruin), not just artifact creatures.

Your version of both these cards will also fail in some rare cases when a card becomes an artifact (or ceases to be one) between it dealing the damage and the damage resolving. A damage source's type at the time it deals damage is stored in a damage card's targets[3].player; its damage_source_player/damage_source_card pair is the source as it currently exists.

Korath wrote:Your version of both these cards will also fail in some rare cases when a card becomes an artifact (or ceases to be one) between it dealing the damage and the damage resolving. A damage source's type at the time it deals damage is stored in a damage card's targets[3].player; its damage_source_player/damage_source_card pair is the source as it currently exists.

The correct behavior is that the damage source still needs to be an artifact creature when the ability resolves to prevent the damage correct?
The cards already do what I am describing. wrong I didn't get what you meant the first time.

edit: fix Argothian Pixies prevents damage from non creature artifacts in commit f139401.

It's complex.

In the 5th-edition rules MicroProse MTG implements, there was a delay between damage being dealt and it being applied, because of the damage prevention step. In theory, at least, you shouldn't be able to play any non-damage preventing effects in between. In practice, they can still happen - sac a Silverskin Armor to Priest of Yawgmoth to add mana for a legitimate damage prevention ability, for example. I don't remember what the correct behavior was then, but at least for colored damage, the program goes well out of its way to remember what color the source was at the time damage was dealt (by setting the color of the damage effect card) rather than looking at its source at the end of damage prevention. Under this interpretation, it should only matter whether the source was an artifact creature when damage was dealt.

(In 4th edition, and I seem to recall the pre-Spells of the Ancients/Duels of the Planeswalkers MicroProse MTG targeted those rules, this sort of effect happened all the time. Damage got saved up until the end of each batch of spells and abilities and there was only a single damage prevention step, rather than there being a damage prevention step after each spell or ability resolved. I haven't any idea whether it was correct to remember the color or type of a packet of damage at the time it was dealt or to look at its source at the end of damage prevention, though again, the care that MicroProse MTG takes to remember the damage's color strongly implies to me that it's the source's attributes at the time damage is dealt, rather than when it resolves, that matter.)

In the current rules, damage happens immediately, and there isn't an opportunity for the source to change colors or types or anything of the sort. Again, the closest Manalink with its separate damage prevention step can come to this is to record the source's attributes at the time it deals damage.

I wasn't playing during the time in between (from 6th edition to I think Magic 2010) when damage went onto the stack. Anyone remember what correct behavior was then?

Anyway, this is all fairly minor nitpicking. The important part of this bug that still needed fixing was that Argothian Pixies was behaving like Argothian Treefolk - preventing damage from non-creature artifacts too.