Let me search for Mossborn Hydra and then figure out which format and archetype context makes sense before running the performance split.
Good, I have the card_id. Now let me check which formats and archetypes are running Mossborn Hydra, and also pull winrate splits for main vs side across all formats.
The data is clear and concentrated in Standard. Let me now get a combined (all-archetype) Standard rollup and grab sources.
Hey @Zacktrack92! Great question. The data from the last three months of Standard tournaments gives a pretty clear answer.
Across 598 total entries in Standard (the format where Mossborn Hydra sees meaningful play, mostly in Mono Green Landfall and Selesnya Landfall), decks running it in the sideboard post a 54.2% winrate (853W-721L across 433 entries), while decks running it in the maindeck only manage 50.6% (286W-279L across 165 entries). That is a 3.6 percentage point gap in favor of the sideboard configuration, and the sample sizes are large enough to be meaningful.
The pattern holds at the archetype level too. In Mono Green Landfall specifically, sideboard Mossborn Hydra sits at 54.3% (363 entries) vs 50.5% mainboard (114 entries). In Selesnya Landfall, the sideboard is 54.4% (69 entries) vs 52.4% mainboard (45 entries). The consistent edge across archetypes suggests Mossborn Hydra functions better as a conditional threat you bring in against specific matchups rather than a maindeck staple.
Sources: Data from 135 Standard tournaments (roughly 75% MTGO, 25% Melee), covering 2026-06-14 to 2026-09-14. Sample events include:
https://melee.gg/Decklist/View/ffd56c98-ac57-46b6-955c-b4c400f1eb05
https://melee.gg/Decklist/View/25afe694-3a8a-492f-8741-b4c400d2d98b
https://melee.gg/Decklist/View/fdbb1bef-54b8-4db8-a3f6-b4c3012c32ca