Depending on how much you want to use the mortars either switch/capacity/capacity or switch/dmg/dmg
Note: since you Need 16.66666% capacity to get 1 mortar, only the combination of boch capacity perks will give you 2 extra mortars (totalling 8), while the gold one will give you 1 mortar and the silver one none.
In both cases the switch is there because, since you have to constantly rotate your weapons, the other perks are just not worth it.
Your shotgun is the main damage dealer. When it’s empty you should throw the frisbee if the weakpoints are not already deployed. Switch to your mortars whenever the opportunity arrises, but also think if it’s worth it. While some Monsters seem to just attract them whereever you aim, others feel like they are impossible to hit. So try to think if it’s really worth it. Or if you could do more damage with your shotgun.
Speaking of your shotgun: It’s an incredibly accurate one. You might have already noticed, but in case you haven’t: you can aim downsights with it, which makes it suprisingly useful at longer ranges. Also it’s already quite accurate (as long as you are not jumping and jetpackboosting).
Lastly, aiming your mortar.
As already said try to not aim where you think the Monster will be, but instead aim where you think your teammate will be, because the monster will be right next to him. Secondly, don’t always shoot every single mortar at the same spot. Try to shoot them in a line, so that when for example a goliath uses his charge, he will charge right through them as they are about to land.
Also, if you stand at the bottom of a cliff or something similar, you can very easily hit a monster, that’s chasing a hunter on top of it or when it’s coming down.
Against a Kraken: there is this one good height where you can directly fire your mortars at the kraken. But in most cases you should stick to the (suprisingly accurate!) shotgun.
Well, that’s what’s coming to my mind right now, maybe I can think of more tips later. Hope it helps, and don’t Forget: