Note that's "cast" and thus happens and cannot be countered traditionally and can be a combat trick to save him from red's burn which is the only thing that can easily answer him or just get him past burn too
Like the majority of Commander-based price spikes, when new legends come along, interest in past cards can fade
The one downside is that this can be not great as an early-game draw, but thats not all that likely in a deck of 99 cards
It cant target creatures, but for burn decks that simply want to reduce the opponents life total, that doesnt matter too much
Your Murktide will get bigger the longer you play, too, with it gaining new +1/+1 counters anytime an instant or a sorcery card leaves your graveyard
Start with cheap common foils from the same set/box and work your way up to the more valuable cards from the same set/box as you perfect your process