Sword of Fire and IceSword of Fire and Ice | art by Chris Rahn

Hello, data enthusiasts, and welcome to this overview of the math behind the EDHREC's Fire Scores, which underpin both the Fire and Ice article series as well as the "Hot" card labels on commander pages.

The purpose of Fire Scores is to identify cards that are either significantly increasing or decreasing in usage with a given commander relative to other cards played with that commander over the most recent six months.

This pages serves as an overview of the math behind identifying these "fiery" (trending up) and "icy" (trending down) cards.

Overview of the Math

We start by looking at all cards that are played with each commander aside from those that are very rare (<2.5% of decks).

We calculate the weekly usage of these cards as a percentage of all decks for each given commander for the past six months.

Then, we determine the slope of the line-of-best-fit of each time series and summarize the data with a single "extremeness" score (also known as a z-score) as follows:

where x = slope of the line-of-best fit for the card trend (% of decks for this commander) over the past six months

Using these extremeness scores allows us to control for the unique deck-building behavior of each commander rather than using a fixed threshold of average change to identify big movers.

We typically identify those cards with extremeness > 2 as "fiery", or having a high "Fire Score", and those with extremeness < -2 as "icy", or having a low "Ice Score", though we may use other extremeness score cutoffs on a commander-to-commander basis.

For identifying cards as "hot" under a given commander, they must have an extremeness score > 2, and upon hovering on the hot label, we provide further detail showing exactly how extreme the score is using fire symbols:

An Example

Let's take a look at card usage in The Ur-DragonThe Ur-Dragon decks over the six month period from September 8, 2025 to March 2, 2026.

The following graph shows a line for each card played with The Ur-Dragon as a percent of Ur-Dragon decks over time.

Another way we can look at this data is relative to the starting point for each card, so now we capture the change in percent of decks. The amount of movement over the last six months starts to become more clear.

We then take the slope of the line-of-best-fit for each card's usage with The Ur-DragonThe Ur-Dragon and look at the distribution of those slopes.

We identify all cards with absolute extremeness scores greater than 2 as fiery or icy, as shown in the histogram below.

If we look again at the absolute usage and relative changes in usage with The Ur-Dragon, we can see these big movers are the ones with the most extreme slopes.

In this case, the icy cards are two popular cards that have been around for a while and are losing steam, while the majority of the fiery cards are new cards released in Lorwyn Eclipsed, except for Mutable ExplorerMutable Explorer and RealmwalkerRealmwalker.

This will not always be the case, but new cards that are highly applicable to a given commander will typically have the strongest fire scores. 

The following table shows which cards were identified as fiery and icy, along with their average weekly changes, Fire/Ice Score, and the number of decks they were played in over the six month time period.

Chomping ChangelingChomping Changeling takes the cake for fieriest card, with a Fire score of 6.25, and Herald's HornHerald's Horn as the iciest card, with an Ice score of -3.02.

Final Thoughts

We hope this overview gives you a sense of how Fire Scores work under the hood. The math is designed to be commander-aware: a card that's surging in The Ur-DragonThe Ur-Dragon decks may be completely unremarkable for a more focused commander where every card is highly curated, and the z-score approach accounts for exactly that kind of variation.

Of course, the math can tell us that Chomping ChangelingChomping Changeling is on fire with Ur-Dragon, but it takes a human eye to ask why. Is it a new set shaking things up? A popular content creator's list going viral? A sleeper card finally getting its due? We speculate wildly on all of the above in the Fire and Ice series, so check it out each week, and keep an eye out for cards labelled "hot" on your favorite commander's page.