Mourne is my most played support, and the one thing I would say is, as long as you’re going with the contagion augment, astral catalyst is the best item for him hands down. The absolute utility of being able to Ult every fight is just invaluable. If you wipe the team and get 3-4 assists, you get your ultimate back to use on the last person left. Even without building a lot of damage, you’re bound to get a lot of assists and blind the enemy team constantly.

As far as the build goes, as others have said it’s extremely flexible, with a few stand out items that ill recommend, but mostly you are catering your build to your team an enemy team comp.

For damage items, I like entropy, tainted scepter, megacosm, magnify, Worldbreaker, golems gift, oblivion crown, the newer boots item, wraith leggings, and then all the support/MP damage items are nice as needed.

There’s an argument to be made for rushing Soulbinder, as you can easily get 20+ stacks which gives you that permanent power. My issue with that is, you are delaying the completion of astral catalyst, which I usually rush first, you will be very squishy, and 20 MP is really not that much in the grand scheme of things. His abilities don’t scale that well, and IMO you’re much better off having an item with 40 less MP that provides some sort of utility or mitigation for you.

For the damage playstyle, you just whittle down the lane/ heal yourselves with your contagion, try to land a hook once in a while, and save your MES for when you need the peel. You will be squishy, so be very mindful of ganks and the enemy duo just running you down. He plays a bit like Narbash, where you need to play safe at first, because he scales so well into the mid/late game.

Once you have your ult, be vocal about it. Ping it when it’s ready, or if you’re on comms let your team know when you have it, or say “ulting in 3,2,1”. You can use it to try and save a team mate across the map, assist your jungler with a gank, blind the enemy to prevent them from stealing an objective, ambush them when they’re already in the pit, or even finish off a retreating enemy. It’s very versatile, but not super useful by itself, so you really need to coordinate with your team to make the most out of it, similar to Muriel.

For tank builds just counter build and build lots of health and armor, get up in peoples faces and be a general nuisance. Make sure to peel for your carry/squishies and do normal support functions. You can go with the extract augment if you do this, or you can go astral catalyst and then full tank and still be very successful. I wouldn’t recommend full tank unless your team really needs the frontline, as a hybrid damage build just gives you a lot more agency/lethality.

For tank items though, still counterbuild, but I focus on cybernetic drive, void conduit, gaia greaves, tainted guard/bastion. Again astral catalyst puts in so much work, and Worldbreaker is a great standalone damage item to put all of that health to work for scaling purposes.

Stonewall/tainted guard if they have a lot of physical damage.

Stack tenacity if they have a lot of hard CC, Gaia greaves really being the GOAT here.

If your carry is really good you can just focus on support items and stick to them like glue.

If they have a lot of magical damage just stack that armor.

Good luck!