Stifle is a tempo card and we are a control deck. we want to tap out and create advantage with powerful cards. stifle will bring you in bad situations because you have to keep your mana open.
more spell pierce depends on your meta.

I played a bigger event at sunday and became third place with 4-1-1.

Round 1: Elves 2-1
He made big mistakes both games. Engineered Plague killed him. The one I lost was against Progenitus.

Round 2: MUD 2-1
A strange player. Playing for many years magic and this deck but not good. often times producing mana to untap grim Monolith and tap it again for 3.

Round 3: Dredge 2-0
First two turn Deathrite Shamans, win. Second game first turn Nihil Spellbomb, second turn containment priest.

Round 4: BUrG Delver 1-2
Very grindy. I lost the last game because I was too greedy.

Round 5: Grixis Delver 2-0
A friend of mine. Sword of Fire and Ice could bring the win.

Round 6: Omnishow 1-1
We managed a draw. I knew he is playing Omnishow and I had nothingn in my Sideboard to win this.