Mawlocs DONT want to be in CC, they are not good in CC at all, they are literally there as a fake (unless they are Mawloc heavy army with 6+ of them).
Tyranids needs to hit you with multiple threats at once, that is how they play, Mawlocs, Genestealers, DSing Devilgants, Harpies, DSing Hive Tyrants, etc..
These are the more dangerous Tyranid lists, ones that will hit you from every angle. the problem with Tyranids are that they MUST support each other, every unit needs a support unit.
Split the army and focus done 1 part of the army, the more you can do this the easier it is to win.
Many players have already said many good things, but as a HEAVY nids player, dont worry about Mawlocs, just put a unit at them in melee and work on them later, kill the real threats right away, this list is from Most important to least important;
Genestealers, Hive Tyranids, Hive Guard, Exocrines, Devilgants, Hgants, Harpies
IMO Harpies are only not being use atm b.c of CWE. IMO Harpies are insanely deadly but not against DE or CWE (due to high damage weapons and Fly keyword for vehicles, against Imperial they are stupidly good, move 30", Bomb, Shoot Lascannons, Charge, fallback, bomb, shoot, charge, repeat).
Devilgants are normal Termagants with 3 shot bolters that has stratagems to make them stronger
Hive Guard and Exocrines are S7/S8 with 6-12 shots that can shoot twice
Hgants seem very weak, but 6" Pile in and Consolidates will tie up many units and objectives at once
Mawlocs are a faint, they look scary, they "can" do MW's (on average only 4 unless you against Orks, IG or other Hordes that they can hit 3-5 units rather than 1-3) but in reality 1-2 of them are there to act tough. So dont be scared of them.
Finally: Unless they are playing 6 Mawlocs, there is a strategy that playing 700pts of them to DS turn 1 along with 3 Hive Tyrants and then having 12 Single Biovores with many ripper units next to Zoanthropes and Venomthropes, in order to MW you down and kill all movement (they will own your realestate), having 8 ish Spore, 6 Mawlocs and the Hive Tyrants all on you and the potential of 50 MW's along with 72 S6 shots and Smites. Its really strong against sow armies (and DE is slow now).
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AoS: BoC 9k, CoS 3k