Monocolor decks can potentially generate a lot of mana to feed into it through mana doublers, but then theres the worry of having to lose that much life as well
In the unusual case where Unwilling Vessel has +1/+1 counters on it and then receives an amount of -1/-1 counters that causes it to die, use the total number of counters that were on Unwilling Vessel when it died, including all of the +1/+1 and -1/-1 counters, to determine the value of X
If you wish to sort alphabetically and remove all the basic lands, you can
The common play pattern of this will be using it offensively and soaking up the crack-back damage, but there will be times where you use it in a more tricksy way by using it as a fog, or even as removal and a fog
However, if you do, and that creature card is an illegal target at the time Mourner's Surprise tries to resolve, it won't resolve and none of its effects will happen