So this actually kind of reminds me of an older team I made once (similar Avalugg + Lando core) which had some struggles with stall, faster necro sets, fairies, and water/grounds. Ninetales is a great third here, as it covers all of those threats and more, and I'm sad I didn't think of it way back then.
Avalugg is a simple straightforward banded attacker, I went with the fast set to have solid odds vs other luggs (the defense improves the roll vs 252 defense sets) and to cover Chansey and Band Aggron. It's really nice for this team and covers a ton of the dragons, grounds, and fast breakers that Ninetales struggles against. It's also a very strong zygarde answer, which this team would otherwise fail to beat. Assault Vest glastrier, which can tank Ninetales with its insane bulk, also loses to this powerhouse.
Ninetales is the LO CM set, because I think it's the best overall and I really like its matchup versus the fairies that are everywhere now. This set has a rock-solid matchup against Necrozma (one of the most spammed mons on the ladder) and can Encore stall into their setup moves. Most fairies, even things like Specs Primarina or Scarf Fini, just can't break through Ninetales' bulk and end up losing to CM-boosted moves.
Lastly there's Landorus-Therian (shoutout to
fruan for helping with the set), which covers Entei, Wisp Pult, those Regidrago variants that beat Lugg, Magnezone, most Spectrier sets, and Zeraora. It also improves the team's overall Togekiss matchup and acts as a secondary dragon counter, making it harder for the opponent to pick into Ninetales. Lando-T should beat every Entei by spamming Rock Tomb and switching to Earthquake once the move connects.
The main issue for this team are unchoiced Urshifus with lots of speed or an Assault Vest. Some Kommo-O sets might also be a problem, and a few Primarina sets require prediction to succesfully navigate. Still, I think it's a solid combination of mons that can do well both on ladder and in tours.