I'll tell you what I look for in a processed card too
Mono-Blue can not ramp up its mana very well and requires extensive use of mana rocks, so Mana Drain adding the mana helps you to start ramping up into your big spells
You know, if you need yet another one for your Satoru Umezawa deck because you dont care who gets attacked as long as you power out some nonsense like Sphinx of the Second Sun
It forces the opponent to either ante the top card of their library or let the outcome of the game be decided by a coinflip
"[Type]cycling [cost]" means "[Cost], Discard this card: Search your library for a [type] card, reveal it, put it into your hand, then shuffle." This type is usually a subtype (as in "Mountaincycling") but can be any card type, subtype, supertype, or combination thereof (as in "basic landcycling")
For example, the black enchantment Black Market Connections provides a nice source of mana, card draw, and tokens with Changeling that will benefit from the Sliver horde's bonus