Teferi, Mage of Zhalfir

Flash
Creature cards you own that aren't on the battlefield have flash.
Each opponent can cast spells only any time they could cast a sorcery.

Venser, Shaper Savant

Flash (You may cast this spell any time you could cast an instant.)
When Venser, Shaper Savant enters, return target spell or permanent to its owner's hand.

Errant and Giada

Flash
Flying
You may look at the top card of your library any time.
You may cast spells with flash or flying from the top of your library.

Draining Whelk

Flash
Flying
When Draining Whelk enters, counter target spell. Put X +1/+1 counters on Draining Whelk, where X is that spell's mana value.

Vega, the Watcher

Flying
Whenever you cast a spell from anywhere other than your hand, draw a card.

Stunt Double

Flash
You may have Stunt Double enter as a copy of any creature on the battlefield.

Winding Canyons

{T}: Add {C}.
{2}, {T}: You may cast creature spells this turn as though they had flash.