Against pantheon, Pantheon is an early to mid game champion and is therefore very strong from levels 1 to 6 and can influence other lanes too when he gets his R.

If Pantheon gets 1 or 2 kills, he can finish Youmuu's Ghostblade and his other core items faster. Pay attention to what active items he has and try to play around them. 

Be careful after the laning phase, as Pantheon will try to kill you with Grand Starfall R and force a 5 vs 4.
 Against pantheon, Pantheon is a champion from beginning to half-time and is therefore very strong from levels 1 to 6 and can influence other tracks also when he gets his R. If Pantheon gets 1 or 2 killed, he can finish Ghostblade from Youmuu and his other base elements faster. Be careful what he has of assets and try to play around them. Be careful after the laning phase, as Pantheon will try to kill you with Grand Starfall R and force a 5 vs 4.