Creatures that bounce on entry, like Cavern Harpy, are also great fits here, nabbing you extra value while you recycle your enters and leaves triggers
26, Feb
Once Ulamog has entered the field, it can truly devastate an opponents whole board thanks to the best Annihilation effect ever printed on an Eldrazi card
Coven is an odd mechanic, in that the only shared feature among all cards with Coven is its requirement: no matter what that card's Coven ability is, it can only happen if you have at least three creatures with differing power (the first number in a creature's bottom right corner)
Since most competitive decks were playing four copies each of Professor Oak (Professors Research without the Supporter limitation) and Bill (draw two cards), players were going through their decks at extremely accelerated rates
Longer answer: Coven is an ability word , and as such it varies from card to card