I need to gather several pieces of data before I can answer. Let me start by getting the Pioneer format meta changes and the Mossborn Hydra card details, then I'll dig into the landfall archetype data.
The user mentioned Pioneer, but the Mono Green Landfall archetype was found in Standard. Let me check if it also exists in Pioneer, and simultaneously look at the meta changes more carefully. The user mentioned "August 2026 bans" but the most recent Pioneer ban I see is from December 2024. Let me check Standard meta changes and also look for the landfall archetype data in both formats. I also need to check if there was an August 2026 ban.
The Standard format has the most recent ban in June 2025, not August 2026. The Mono Green Landfall archetype exists in Standard. Let me now search for August 2026 bans more carefully - they may not be in the database yet. I also need to check Standard for dimir tempo and get the matchup data. Let me now pull archetype data specific to Standard and look for the relevant archetypes, and check Mossborn Hydra adoption in the mono green landfall deck.
Now I can see the current Standard meta. The user mentioned "August 2026 bans" but I don't see any bans in August 2026 in the Standard meta changes (last ban was June 2025). The meta also shows no "4c control", "azorius control", or "dimir tempo" as top archetypes - the meta has Mono Green Landfall as #1. Let me now get specific data: Mossborn Hydra adoption in Mono Green Landfall (main and side), and matchups vs the archetypes the user mentioned.
Excellent! Now I have the key data. Let me now get the matchup winrates vs the archetypes the user mentioned, and also query the database to compare performance of Mono Green Landfall decks with Mossborn Hydra in main vs side vs neither.
Now let me query the database to compare winrates of Mono Green Landfall decks with Mossborn Hydra in main vs sideboard vs neither.
The win/loss result data appears to not be populated in the matches table directly. Let me try a different query approach using wins/losses from tournament_entries instead.
That's very telling data. But I notice there's no "NONE" row, which means every entry has Mossborn Hydra somewhere. Let me also check for entries with no Mossborn Hydra at all, and also verify average copies in side for the SIDE group.
Now I have all the data I need. Let me also note that there's no "NONE" group, meaning all 247 entries (71 + 176) have Mossborn Hydra somewhere. The data is very clear. Let me compile my answer.
A note on framing: The user mentioned "August 2026 bans" - but the database shows no bans in August 2026 for Standard. The archetypes they listed (4c control, azorius control) don't appear in the current Standard meta top 20 either - the closest things to control are Jeskai Control and Jeskai Lessons. "Dimir tempo" is also not present as a named archetype, but Dimir Midrange and Dimir Excruciator are. I should flag these discrepancies while providing the data-backed answer.
Hey @Zacktrack92, great question. Let me flag a few data points that differ from your framing before diving in, then give you the hard numbers.
First, on "August 2026 bans": the database shows no bans registered for Standard in August 2026. The most recent ban wave on record is from June 2025. The current meta context I'm working from is post-August 2026 set release (Edge of Eternities, August 2025), which is the last tracked meta change. If a ban happened after that date, it has not yet been reflected in the database. Second, the archetypes you named don't map cleanly to what's in the data. There is no "4c control," "azorius control," or "dimir tempo" in the current Standard meta. The closest analogues are Jeskai Control (7.6% presence, 52.8% WR) and Dimir Midrange / Dimir Excruciator (~6.7% and 6.3% presence). I've used those as proxies.
Now to your actual question, and the data here is pretty unambiguous. Looking at 247 Mono Green Landfall entries in Standard from August 1 to September 7, 2026:
Mossborn Hydra in the SIDEBOARD: 176 entries, 56.87% winrate (360W / 273L), averaging 3.9 copies sided. This is the overwhelming consensus among players, appearing in 87.5% of all sideboards.
Mossborn Hydra in the MAINDECK: 71 entries, 50.22% winrate (116W / 115L), averaging 2.66 copies in main. Only 28.7% of lists run it main.
The gap is stark: sideboard Hydra players win at 6.65 percentage points higher than main-deck Hydra players, and the overall archetype winrate sits at 55.1% for context. The tournament community has clearly converged on the side as the correct home for it, and the results back that up. The Hydra is likely excellent in specific matchups (Jeskai Control, where you have a squeaky 52.3% WR, and the Dimir-adjacent decks where you go 61.97% and 61.67% respectively), and running it main may dilute your proactive gameplan against the field while not adding enough when you don't need it.
Bottom line: keep Mossborn Hydra in the sideboard. The data says side it at a high density (3-4 copies), and bring it in surgically against the control and tempo matchups.
Sources: Data from 50 Standard tournaments between Aug 1 and Sep 7, 2026 (74% MTGO, 26% Melee). Recent events include: