Before the really long stuff, for the first few lines you dont have to spam the noob, and you can name your timers so you dont unset all.
Next time use the var command instead of set, so you dont have to unset it after, Var %chanced $nick - No need to unset after.

on *:TEXT:!RiskRoll:#:{
  if ($nick = %chanced) { 
    if (%chancenum == 1) {
      msg $chan 0,1You've passed. Way to go! 
      unset %chanced
      timer* off 
      halt
    }
    if ($nick = %chanced) {
      if (%chancenum == 2) {
        msg $chan 0,1You fried to a crisp D:
        unset %chanced
        timer* off
        halt
      }
      if ($nick = %chanced) {
        if (%chancenum == 3) {
          msg $chan 0,1You exploded. That's gotta hurt!
          unset %chanced
          timer* off
          halt
        }

You probobly put the { in at the end and missed a closing bracket for each of them. Count it off :)!

on *:TEXT:!RiskRoll:#:{
;1
  if ($nick = %chanced) { 
;2
    if (%chancenum == 1) {
;3
      msg $chan 0,1You've passed. Way to go! 
      unset %chanced
      timer* off 
      halt
    }
;3
}
;2
    if ($nick = %chanced) {
;2
      if (%chancenum == 2) {
;3
        msg $chan 0,1You fried to a crisp D:
        unset %chanced
        timer* off
        halt
      }
;2
}
;3

      if ($nick = %chanced) {
;2
        if (%chancenum == 3) {
;3
          msg $chan 0,1You exploded. That's gotta hurt!
          unset %chanced
          timer* off
          halt
        }
;3
}
;2
}
;1

Try thtat instead.