I used to play with them when I was a kid but now they just sit in the bottom of one of my closet and collect dust
Any colored mana costs must be paid by the spells controller, even if the assisting player paid mana of that color
Much of what Im going to say he touches on in there, but my ideas actually came from grinding playtest games where turn 1 Thoughtseize happened probably far more than it should have
Four-Color Control (5 players): This deck controls the game with spot removal like Prismatic Ending, countermagic like Counterspell, and planeswalkers like Teferi, Time Raveler, while splashing for two or three copies of Omnath, Locus of Creation
The problem with that version of Nicol Bolas is that there are many incentives to take advantage of its special ability with things like Dragon Tempest or Psionic Gift when thats your commander
Even if you have no other counters in play when you bring out your Contagion Engine, it provides a large amount of -1/-1 counters which you can then multiply using its proliferate effect