If you have some Standard staples that will be rotating soon, you should try and trade them before rotation: Their prices will usually drop post-rotation
You can have as many copies of Rat Colony as you want, even in singleton formats like Commander
It fits slower midrange or control builds and pairs nicely with artifact synergies like Thorough Investigation, turning Clues into both cards and combat incentives
The player attack restriction gives it the feel of turning each players allies against them, which is deliciously evil
Before Modern Masters release: ~$50 Four months After Modern Masters: $75 Dark Confidant is an interesting case study from Modern Masters
(If a permanent with a stun counter would become untapped, remove one from it instead.) Drowned Diner Three generic, two blue enchantment Room Common (You may cast either half