Good, I have both the archetype ID and card ID. Now let me query the database to compare winrates for entries with Mossborn Hydra in main vs side.
The entries are found but match data isn't joining correctly. Let me fix the join to use the correct match linkage.
Result values are WIN/LOSS/DRAW. Let me redo the winrate query with the correct values.
The data is clear. Here is the answer:
Versions with Mossborn Hydra in the sideboard significantly outperform those running it in the main deck. Across all Standard tournament data in the database:
Sideboard Mossborn Hydra: 960 entries, 54.8% winrate (2663 wins / 2195 losses, excluding mirrors and draws).
Main deck Mossborn Hydra: 356 entries, 48.3% winrate (809 wins / 867 losses, excluding mirrors and draws).
That is a 6.5 percentage point gap in favor of the sideboard version. The sample sizes are substantial enough to be meaningful. The sideboard version also sees nearly 3x more tournament play, suggesting the community has broadly converged on keeping Mossborn Hydra out of the main. It appears to function best as a targeted answer to specific matchups rather than a general-purpose threat in the 75.
Sources: Data from 104 Standard tournaments (80.8% MTGO, 19.2% Melee). Recent examples include the ReCQ Standard at SCG CON Dallas (2026-09-06): https://melee.gg/Decklist/View/c03ebfbc-9056-4696-872d-b4bd012250f2