You should be able to build your deck to maximize the turtle without compromising it to settle for creatures that aren't playable
Even if youre not in the dedicated mill plan, theres still good value to gain from Shinra Reinforcements
1 Underground River 7 Swamp 7 Island 1 Tamiyo, Inquisitive Student 1 Nethergoyf 1 Cecil, Dark Knight 1 Sinkhole Surveyor 1 Caustic Bronco 1 Dauthi Voidwalker 1 Gix, Yawgmoth Praetor 1 Preacher of the Schism 1 Emet-Selch, Unsundered 1 Fallen Shinobi 1 Shriekmaw 1 Cling to Dust 1 Portent 1 Ponder 1 Consider 1 Inquisition of Kozilek 1 Bloodchiefs Thirst 1 Stormchasers Talent 1 Heartless Act 1 Sheoldreds Edict 1 Long Goodbye 1 Winternight Stories 1 Stock Up 1 Control Magic 1 Snuff Out It looked great there when it was played
Burn is one of the tougher matchups for Mono-Red Phoenix, as Eidolon of the Great Revel is one of the best cards against the deck
Im not sure its quite worth 6 mana, but maybe
For the everyday casual folk like me, this is just a boring commander