Hey, nice upgrades for the precon.

There's several cards that are in the sideboard that are better than cards in the main deck specifically the hexproof creatures. Mutate is very problematic in multiplayer Commander because there's at least three other players who can have removal for the mutate creature. If you're not mutating a hexproof creature then removal options from three or more different players is too much of a problem. Mutating turn four like what you want to do is too risky if you're not mutating a hexproof creature.

The combination of hexproof and regenerate is very good with mutate. Protection from first being able to mutate, then after from targeted removal, then also from most board wipes and combat. Constable, Needle and Selkie are powerful if they connect with an opponent when mutated, but using them as the creature to mutate too for turn four is risky without also having protection.

Some changes to consider:

• Slippery Bogle > Hungering Hydra
• Silhana Ledgewalker > Ilysian Caryatid
• Troll Ascetic > Butcher Ghoul
• Thrun, the Last Troll > Pouncing Shoreshark
• Crystal Shard > Ram Through
• Jarad's Orders > Frontier Siege
• Nature's Lore > Rampant Growth
• Exotic Orchard > Vivid Grove
• Yavimaya Coast > Thornwood Falls
• Woodland Cemetery > Jungle Hollow

Good luck with your deck.