The opponent would start his upkeep, scute mob's ability would
go on stack, you react with sudden spoling, at which point scute
mob becomes 0/2 and loses all abilities. This won't prevent the
ability already on stack from resolving tough, so if he has 5 lands
or more scute mob would get 4 +1/+1 counters leaving him a 4/6 for
the rest of the turn.