I've been having some trouble with nekkers too lately. Even when i used my NG deck with Peter i lost, as now the Nekker players know how easy it is to reset and banish one, so they have tons of backups!
Before, i usually only had to deal with 4-5 Nekkers, so i left it for the end and banished at the end, but on this patch i've had matches where i saw 9-10 Nekkers, didnt really know how to stop that.
Not even my Kambi deck, that is usually my last resort and works against almost everything saved me, as killing those 2 nekkers on board only brought 2 of the same pts, + Hemdall = 40 something points!