Players can respond to this ability triggering, but once you choose a creature to sacrifice, it's too late for anyone to respond
If the game gets incredibly grindy, Aetherflux Reservoir is there to annihilate players once you have enough life
Milling your opponent is actually positive for them unless you can finish them off, and there simply isnt enough lifegain to enable Hope as a potential win condition
Other dealers will sometimes have the box or binder of damaged goods, and Im telling you to always check such things when they show up, for two very good reasons: Value or Budget Look, we arent all big spenders

(Click the following to see the deck's tokens and helper.) Wakanda Forever Tokens 3x Vibranium // Angel tokens 2x Soldier // Goat tokens 2x Soldier // Copy tokens 1x Vibranium // The Monarch (helper) token 1x Rhino // Elephant token 1x Rhino // Beast token 0015a_MTGMSH_CmdrTkn: Vibranium Token // Angel Token 0004a_MTGMSH_TknBstr: Soldier Token (Wakanda) // Goat Token 0004a_MTGMSH_TknBstr: Soldier Token (Wakanda) // Copy Token 0015a_MTGMSH_CmdrTkn: Vibranium Token // The Monarch (Helper) 0013a_MTGMSH_CmdrTkn: Rhino Token // Elephant Token 0013a_MTGMSH_CmdrTkn: Rhino Token // Beast Token (Back) The Fantastic Four 0001_MTGMSH_CmdrFace: Invisible Woman 0002_MTGMSH_CmdrFace: Mister Fantastic 0003_MTGMSH_CmdrFace: Human Torch 0004_MTGMSH_CmdrFace: The Thing Invisible Woman Mister Fantastic Human Torch The Thing Galactus, Devourer of Worlds Silver Surfer, Galactus's Herald Invisible Force Field Ultimate Nullification Council of Reeds Fantastic Elasticity Lockjaw, Slobbering Teleporter Valeria Richards, Precocious Alicia Masters, Skilled Sculptor Flame On

Its also worth mentioning that these errors can happen across multiple cards