We want cards that make sense. While thats the starting point, he also says they dont want to spend a lot of time and energy putting gorgeous, amazing art on cards that we dont think anyone would ever want to do anything with, meaning playability is also a factor to some degree
(2014-07-18) If enough -1/-1 counters are put on Chasm Skulker at the same time to make its toughness 0 or less, the number of +1/+1 counters on it before it got any -1/-1 counters will be used to determine how many Squid tokens you get
Each option had to be able to be cast at instant speed, and they all needed to be mono-blue
The more accurate a card is to the concept it's representing, the more complex it usually is
If it tries to put an instant or sorcery card onto the battlefield this way, that card remains in its current zone instead
Keep an eye on ban announcements in competitive formats, too