Soulflayer did not gain hexproof from mono-colored and trample over planeswalkers when it delved Sphinx of the Guildpact and Thrasta, Tempest's Roar.
According to Soulflayer's ruling from the gatherer it should work.

Soulflayer delved Sphinx of the Guildpact and Thrasta in the graveyard

Actual: Soulflayer only gained flying, haste, and trample.

Expected: Soulflayer should gain hexproof from mono-colored, trample over planeswalkers, flying and haste.