My plan against Dredge:
+2 Ravenous Trap
-2 Hollow One
Leyline is certainly the most effective way to combat Dredge, but I'm not yet willing to sacrifice my well rounded SB (and plans) against most of the field just to get more edge against Dredge.
Manglehorn has found it's way back to MB because PO is a problem and Karakas is very effective against all the legendary hatebears. For the same reason I'm now running two Mindbreak Traps as often even Lavinia combined with a Stony Silence has not been enough to win the game. Fast combo is certainly an issue, but I do enjoy the play style of this kind of build (i.e. make them have the answer instead of trying to fight on stack). And so far my record against PO is good enough with plenty of games under my belt against it that no drastic measures need to be taken.