Morgana

While she can counter your ult, morgana is not a very powerful champion otherwise. Many believe that she is a hard-counter, but most of the time you can just ignore her, especially with MR Boots. You also have good damage to burst her shield early and don't have to be scared of engaging because of her E. If she uses it, simply walk away and wait for the next engage

Thresh

Thresh is a hard matchup and generally counters Nautilus. However, he is also immobile himself. I recommend playing around your teammates and consider going for tenacity. Try to play around his E+Hook combo, by not standing near his range too much. If you hook him, try to reposition so you cannot be hooked easily

Sivir

She can blackshield your hook but you can still CC her with your other abilities. If she blocks your hook, walk away or look for R if possible

Brand

He has very high damage especially if he hits you with his whole kit. Try to look for cheeky hooks and consider instantly repositioning after landing, always anticipate that he will use his kit after you hook. Try not to stand around or go for passive proc immediately

Alistar

He is very tanky so not really worth hooking and he can also engage/disengage quickly. Alistar is a disengage champ so he generally has a slight advantage. Look to R his teammates. You can also cancel his engage yourself if timed correctly

Ezreal

While he is mobile he is pretty weak and should die most of the time when he is hooked while his E is down. You can also hook and R immediately, or R him on sight. Many ezreals make the mistake of getting hooked on purpose to E, but often you can still get your slow off him or follow with R

Yuumi

Yuumi can't really do anything against tanky engages. She can be strong depending on ADC however so do respect her Q poke

Heimerdinger

His turrets can be annoying since he can use them to block hooks so wait for ult if you can't reach him and ask for ganks

Braum

Nautilus biggest threats are enemies that benefit from stopping your engage, then engaging themselves onto your own team. This is pretty much braum's nature, making him a tough matchup. I recommend not overforcing against him, as he will benefit from retaliating. You can look for hooks to force his E but immediately walk away once they land

Rakan

Rakan is a strong counter to Nautilus. Try not to let him heal too much using Q, and look for stopping his W with hook. I also recommend not wasting your aftershock on hooking him, as he will just E to his ally

Blitzcrank

You can stop his hook by using Q on the wall. He is also not very powerful since you can easily block his path and provide peel for ADC. Beware of getting caught however

Amumu

Bard

He should not be able to do much against you, he is also very vulnerable to getting hooked.

Zyra

Respect that she can block your hooks and deal a lot of poke. She is still immobile and squishy herself so look for cheeky hooks out of bush, take bush control early but don't get poked too much and try to respect her early. At 6 you should easily begin winning.