add advice on op casters

gm.tex

@@ -414,6 +414,19 @@ Once multiple goblins are attacking as a Sneak Attack, they'll each receive +4 t
 Remember to attack whichever \gls{pc} is the strongest in order to lower their initiative.
 Once a \gls{pc} has run out of initiative, keep attacking so that the \gls{pc} gets a penalty for defending while below 0 initiative.
 
+\subsubsection{Magical Chicanery}
+
+At some point, the party spellcaster may put together a \textit{Massive, Range, Sentient, Murder-Spell}, and destroy anything in their path.
+This isn't a breach of the rules -- it's just good use of them.
+
+Firstly, remember that \glspl{xp} is limited to the first three creatures killed in a single go.%
+\footnote{See \nameref{xpCreatureMax}, page \pageref{xpCreatureMax}.}
+Secondly, it's time to up the ante and miss out encounters.
+If the party mage can handle 30 goblins with a single spell, just gloss over goblin encounters with a brief roll of the dice.
+If the party mage somehow fails the spellcasting roll, run the encounter; otherwise, move on.
+Focus on the encounters that still matter.
+There are always creatures big enough to challenge a caster of any magnitude.
+
 \end{multicols}
 
 \section{The Players}