Your triggers leaks location, leaks group and conditions for group creating are wrong. (Units within 300.00 of VanGrd_Temploc matching (((Picked unit) belongs to an enemy of Player 11 (Dark Green)) Equal to True))
If you see 'matching' (matching condition) you have to use 'Matching unit' reference. Picked unit refers only to actions that 'pick' units.
Man, why you set a group, and use action Pick all units in group - without selecting group you have just created? You don't need to set group anyways, since I see you remove picked units instantly so its only temporary group.
Unit - A unit Starts the effect of an ability
(Ability being cast) Equal to Vanguard's Smash
Set VanGrd_Caster = (Triggering unit)
Set VanGrd_Temploc = (Position of (Triggering unit))
Custom script: set bj_wantDestroyGroup = true
Unit Group - Pick every unit in (Units within 300.00 of VanGrd_Temploc matching (((Matching unit) belongs to an enemy of Player 11 (Dark Green)) Equal to True)) and do (Actions)
Loop - Actions
Unit - Cause VanGrD_Caster to damage (Picked unit), dealing (6.00 x (Real((Strength of VanGrd_Caster (Include bonuses))))) damage of attack type Normal and damage type Normal