Setup:<ol><li>Install <a href="https://cockatrice.github.io/">Cockatrice</a>.</li>
<li>Download <a href="17.m17.xml">17.m17.xml</a>.</li>
<li>Import `17.m17.xml` via Cockatrice menu bar → `Card Database` → `Add custom sets/cards`</li></ol>
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Deckbuilding:<ol><li>Paste your booster contents into a text editor and save as a *.csv file, then open in Excel. Or, paste directly into Excel and do `Text to Columns`.</li>
<li>Sort by columns A then F then B then E, where E is a reverse sort.</li>
<li>Track the cards you're maindecking by typing `1` in column G. You can highlight the column and look at the sum to get a count.</li>
<li>When you're done, sort by column G, then highlight only column D of the cards you're maindecking, and copy-paste into another text file. You can add sideboard cards by prefixing `SB: ` like `SB: 1 Elixir of Memories`.</li>
<li>Save your text file in Cockatrice's decks folder. For me it's `C:\Users\Xom\AppData\Local\Cockatrice\Cockatrice\decks`</li></ol>Sorry there doesn't exist a better deckbuilding interface that supports custom cards.