Alright so i understand the rule that if you have +1+1 counters on a creature and something tries to place -1-1counters on it they will basically remove each other.
Yes. Continous effects from static abilities like that of Liliana's Mastery work only and as long as the object that creates it is in the right zone. Usually, this is the battlefield. But if the ability specifies otherwise or couldn't work from the battlefield, the ability works while in that specified zone or the zone it can work from.
In your scenario, once Liliana's Mastery leaves the battlefield, its effect giving +1/+1 to Wayward Servant (and other Zombies you control) ends (C.R. 611.3b, 611.3, 112.6), but the -1/-1 counter on Wayward Servant remains, so that Wayward Servant is now 1/1 (C.R. 613.1g, 613.3d, 613.1, 613.4).
But my question is.
Let's say i play liliana's mastery so my other zombie cards all get +1+1 so my wayward servant is a 3/3 now
Now my opponent plays splendid agony and puts 1x -1-1 counter on wayward servant he is now a 2/2 and the counter STAYS ON correct?
So your Servant is currently a 2/2, and the -1/-1 is not removed.
Now if lilianas mastery would get killed..
Does the servant become a 1/1?
Yes.
A creature's P/T is constantly being calculated, taking in account anything that currently exists changing it.
Before it was a base 2/2 with a +1/+1 effect and a -1/-1 counter, for a total 2/2.
With the Mastery gone, you recalculate it as a base 2/2 with a -1/-1 counter, for a total 1/1.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
In your scenario, once Liliana's Mastery leaves the battlefield, its effect giving +1/+1 to Wayward Servant (and other Zombies you control) ends (C.R. 611.3b, 611.3, 112.6), but the -1/-1 counter on Wayward Servant remains, so that Wayward Servant is now 1/1 (C.R. 613.1g, 613.3d, 613.1, 613.4).