If at least one part of the merged creature got through it's summoning sickness, then it can attack or for abilities
Contagion Engine is extra deadly because it gives out two poison counters per activation
Howling Mine is the cheapest to cast, allowing for very early card draw, but its also reciprocal, thus speeding up your opponent as well
Enchantments have always been a less playable card type than artifacts, making Ray of Revelation a bit less exciting than Ancient Grudge historically, but Ray of Revelation is every bit as effective when needed
Rumors of it coming up for sale do occasionally crop up, such as the fake, now taken down eBay listing for $200,000 in 2017, but nothing official has been confirmed since 2001
All five colours is the most difficult casting cost you can possibly put on a Magic card, says Heggen