BiggusGeekus said:
			
		
	
	
		
		
			I lobbed a slow spell at them and described it as the asphsalt reaching upward and entwining the PC's legs.
		
		
	 
I had a homebrew magic system in which the mechanics of a spell could be known (skill check to use successfully), however the actual effect could be quite arbitrary.
So, for example, a wizard could state he wants to target the 10ft space (target) 20 ft ahead of him (range) with a spell that reduces the speed of anyone entering it by half (effect ie Slow Speed) the effect to last for 10 minutes (Duration) the result could include being entangled by asphalt, sinking into quicksand, or increasing gravity (so opponent becomes ultra-heavy) or anything else imaginable.
A Thematic could be invoked (so a Water mage could be created and in the above case use the quicksand option). It was also possible to have the same effect using different Disciplines (School Specialisations) eg Flight could be achieved using 
Psionic Levitation  (Manipulation), 
manipulating wind currents  (Manipulation), 
Overcoming Gravity  (Alteration), by 
Sprouting wings  (Transformation) or by taking on 
gaseous form  (Transmutation) etc
another example
A wizard Conjures a instantaneous 2d10 damage dealing spell in a 50 ft space 100 ft away 
For Kohl the Fire Mage this is a Flaming Maelstrom
For Magret the Druid this is a Hail of Thorns
For Azra the StormWarden this is a Arctic Blast 
(same mechanics different effects)
Of course Kohl could have used his Manipulation discipline to take a normal camp foire and have it become a 2d10 damage dealing spell in a 50 ft space 100 ft away
(ie say effect different mechanics)