This build is extremely fun, you just run around and stun people with Everfrost then run back at them with W and 1 shot their ***.

Everfrost on Lillia is underrated. You get more cc, alot of AP and you get some AH.
When ganking with Everfrost you don't have you use smite or have your passive stacks up even if your laner doesn't any cc. Combined with HF you get ALOT of damage if you hit the root, so you get a huge 2 item powerspike

As said earlier HF works very well with Everfrost and also with your R and E. If you proc the HF passive you are almost guaranteed to 1-shot whoever you proced it on.

Demonic Embrace on Lillia is something mostly everyone should build no matter what you are trying to do. The extra survivability you get with this item is insane. When you also take the burn into conisderation this item just becomes to good to not use on Lillia.

This item should be self explanatory, you get bonus MS and AH(which let's you stack you passive faster for more MS). This makes it so you can keep doing what Lillia does, running around healing what little damage she takes because nobody can hit her.

Also self explanantory, this Item gives alot of AP which is damage(obviously) and also gives more MS on your Q passive.

Start either red or blue depending on which one the enemy jungler starts at. You want to mirror your opponent in most cases. So if they start red you also start red. We do not want to fight for crab in alot of matchups.

Try to get off a gank on mid or the sidelane, but not getting anything for it is not a big deal. This build is 90% gonna get you back into the game even tho you went AFK for 10 minutes(I have tested).

In the Mid Game is where you start to get some damage. You can now run around melee champs and not get hit by a whole lot while healing the damage you take back up with you passive and Ravenous Hunter. Your main combo here is Everfrost into E-W-Q or E-Q-W Depending on what you like or if there are multiple people around you, if there are multiple people around you you would use E-Q-W to get Q damage of onto as many people as possible and then using W to kill whoever is low. In some cases you also want to use you E on the way out or use if they get away using QSS-flash or something similar to that.

At this point of the game you just wanna clear your jungle as fast as possible(which is really fast). If you see a small chance to get a kill go for it. You will realise how much kill potential you have with these 2 items and get alot more kills than you expect if you play it correctly.

At this point you should have been able to end unless you have no team. My personal experience at this point of the game is limited so I can't really give a proper guide or anything like that. What I have seen from the limited time I have been at this part of the game is that your E is mostly what you want to engage with. If they have a spellshield like Malzahar passive you will pop it but not get off your passive on him. When this happens you could run in and Everfrost into Q-W but this is obviously a bad idea if there are 2 or more people near the person you hit. So instead you could wait for E again since it has a low cooldown, then R into you combo. This is helpful for creating more opportunities for you team. This is not ideal in alot of cases tho since you have like 500 MS on like 1 second CD on you Q you could instead run around hitting 3 or more people and then using R to get off a massive engage.