Theyre colourless, a callback to the nature of Eldrazi first explored through devoid back in the Zendikar block, as they transcend normal coloured mana
Bonus Secret Lair cards = Bonus value
(You cannot halve the same damage twice this way.) While you control a Link Monster, monsters your opponent controls cannot target monsters you control for attacks, except this one, also your opponent cannot target monsters you control with card effects, except this one
Its effect to sacrifice ten nonland permanents to deal ten damage to each opponent can sometimes come in handy in a pinch to close out a game
If you can quickly and easily turn them face-up, like with Hauntwoods Shrieker, this shower of +1/+1 counters could give you the gas you need to end the game soon after
A Step Towards the Modern B&R WotC finished the year 1996 with an interesting announcement