The exile clause is the most important part about this card, which is super useful for getting rid of cards like Memory Deluge, Squee, Dubious Monarch permanently
Ashcoat of the Shadow Swarm | Illustration by Christina Kraus Rat is a creature type in Magic that's been around since the very first set
When mixed with a card like Deadly Dispute (which Ichor Wellspring is the main target to sacrifice for Deadly Dispute's effect), you get to draw multiple cards to get a nice refresh of your hand while ramping
It wont go in every deck, but itll be easier to execute than Angel of Destiny if you build it right
If an effect allows an opponent to cast spells any time they could cast an instant (for example, if your opponent controls Teferi, Mage of Zhalfir), the restriction of Teferi's last ability takes precedence over that permission
Broadly, there are two types of counterspells in Magic: hard and soft. Hard counters stop spells in their tracks without any restrictions, while soft spells either only stop the spell temporarily, or have an option to bypass the counter