Ramses, Assassin Lord, asks you to kill one player at the table in order to win the game
Anyways, we saw Slivers in that take, with them hitting Rath Block, and later Onslaught Block and Time Spiral Block
Creatures you begin to control later in the turn won't gain any abilities or cause creatures to gain new abilities, and the abilities gained won't change even if every creature that normally had the abilities leaves the battlefield
Melek, Izzet Paragon is the epitome of a Commander that youd want to play to copy your instant and sorcery spells
If you do, Cryptoplasm gains this ability
Much of the talk Ive seen so far has involved Nethroi, Apex of Death (some it from me) and Illuna, Apex of Wishes, but I suspect that well see some creative builds from the community with the others as well