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DRAMATIS PERSONAE:

[[Gideon Blackblade]] ............... Hero
[[Dauntless Bodyguard]] ........... Stunt Double
[[Vraska, Golgari Queen]] ......... Villainess

On my opponent's turn, my opponent casts Dauntless Bodyguard choosing his only creature at the time, a creature-form Gideon Blackblade (as per his passive ability). Dauntless Bodyguard's oracle text is as follows:

As Dauntless Bodyguard enters the battlefield, choose another creature you control.
Sacrifice Dauntless Bodyguard: The chosen creature gains indestructible until end of turn.

On my turn Gideon reverts back to Planeswalker form and I cast Vraska to use her -3 ability to destroy Gideon. In response, my opponent sacs Bodyguard to save Gideon but no effect occurs, and Gideon dies.

I try this scenario out again against Sparky using a plains that has been animated with [[Sylvan Awakening]], casting Bodyguard, waiting for it to stop being a creature and trying to kill it using [[Memorial to War]]. When I sacced Bodyguard the Plains did not gain indestructible and was subsequently destroyed.

However, multiple judges have stated that the opposite should occur:

https://www.cardmarket.com/en/Magic/Insight/Articles/CMAskTheJudge-Episode-40-Guarding-the-Hero

https://magicjudge.tumblr.com/post/174959330247/if-i-have-dauntless-bodyguard-protect-a-crewed

After consulting with a judge chat I was made aware of the following in the comprehensive rules:

700.7 If an ability of an object uses a phrase such as “this [something]” to identify an object, where [something] is a characteristic, it is referring to that particular object, even if it isn’t the appropriate characteristic at the time.

Example: An ability reads “Target creature gets +2/+2 until end of turn. Destroy that creature at the beginning of the next end step.” The ability will destroy the object it gave +2/+2 to even if that object isn’t a creature at the beginning of the next end step.

So Bodyguard should've been able to grant indestructible to his non-creature friends.

Is there something else entirely that I'm missing, or does Arena have this interaction wrong?

External link →
over 5 years ago - /u/WotC_BenFinkel - Direct link

Thanks for the report - I've confirmed that the Indestructible-granting layered effect is indeed constraining its recipient to be a creature incorrectly. I'll fix this up today. #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by igot8001

Can somebody explain why this works differently than, say, prevention effects (other than the fact that the behavior of prevention effects is explicitly codified in these instances)?

It's more about what "the chosen creature" means. It's actually lies, as rule 700.7 quoted by OP indicates. It really means "the chosen game object", but that reads worse in English. The problem is that the Arena rules-parser is using that English to write the ability's code, so... #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by DragonXDoom

Out of curiosity, is the code for each card parsed from English, and then can be manually altered?

To put the question another way, to fix this bug, are you changing the card or the parser?

Thanks in advance! :-)

The parser. I like to describe my job as teaching a computer how to read M:tG cards. #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by AnalphaBestie

I can imagine that writing software to parse magic cards is absolutely great and terrifying at the same time.

You are correct on both fronts. :D #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by HackworthSF

Can you share some details on how the parser works? I've heard of people training neural nets to do the job, though I suppose you developed an "MtG grammar" that can break down the abilities of most modern card deterministically. Or something else entirely?

Neural nets are a bad fit for the problem because they're pretty "noisy" - they have lots of potential to make pretty much undiagnosable mistakes. We have a pretty classic-AI approach - a spelled-out grammar and dictionary that covers all of the rules texts we support, and a system that takes the resulting syntax trees, gleans their semantics, resolves anaphora (e.g. what does "it" mean?), and compiles the resulting ambiguity-free instruction flow into the final code. #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by JoeScylla

As a software developer myself, i find this very interisting. It's that kind of solutions that nobody thought off and after someone implemented it - it kinda feels obvious solution to this problem.

Can you (are you allowed to) share some trivia about this? Who had that idea? Did you know this will kinda work out or did you do a prototype? How satisfied are you with this solution - how good does it work - how many work does this save to add a new set?

Many of the things you want to know are from before my time (Arena's was quietly in development for quite a while!). It's hard to really estimate how much work this solution saves per set - after all, we've never done a set for Arena without using this system. As a general rule of thumb, a set has around 75% of the cards in it work right away with no need for developer work, around 10% work with less than a couple hours of work, 10% need around a day, and 5% are really hairy. #wotc_staff

over 5 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by thesalus

Is it a possibility to use errata to address particularly gnarly text? Or is that a blunt instrument tantamount to admitting defeat?

Yes to both. It's almost always "hidden errata", or what we call a substitution. Just the parsed text is changed, the displayed text remains the same. [In Oketra's Name] is my favorite example of a card we subbed, to change "other creatures" to "non-zombie creatures".#wotc_staff






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