Finished all achievements for Liberty Campaign..?

Basically, before the first attack wave, kill off the zerg stuff on your expansion, then expand there while waiting for the first timed attack wave, use the HT you get from the warp gate to snipe the overseer that's guarding all the infested terrans, bring an observer or a couple colossus (I went with colossus to guard the HT cause I didn't want him to die) to spot the high ground, blink Zeratul up, blink Zeratul down, grab the tendril, blink back up, blink down and go home to your base with probably a minute to spare before the first attack. You should have a couple of stalkers and your tech buildings by now. Defend the wave (I got super lucky and it was only one worm that was where I was keeping Zeratul, got no zerg spawn from it, just locked it down and killed it).

Use the HT and the three stalkers + any stalkers you have leftover combined with your two colossus to push the left side, push up the ramp and into the zerg base that is beyond the 2nd obelisk (abuse the high ground if you want to, I just marched in through the choke), you can ignore the zerg camping by the robotics bay. Make sure to blink-kill the broodlord I encountered here, dunno if it's camped or patrols. Clean out that base and by the time you are done your second wave of stalkers (bringing it to about 12-15 which is PLENTY) and colossus (you should have 4-6) will arrive about the same time as the next attack wave (ignore defending your base, obviously). Push down the ramp into the flyer camp, there's many mutas here and I encountered one broodlord, just snipe it with 5-6 stalkers then pull them back to the rest of your force for when the mutas attack (I pulled four or five or so in one go). Slowly crawl your obs/colossi up the ramp to spot, nuke off any spine crawlers so you can kill the spore crawlers safely while you Feedback any overseers, blink Zeratul into the circle (you can basically blink him once as soon as he is up the ramp and he can run the last bit without trouble at all).

In the end I think I overcomplicated things a lot by being too careful, two colossi can hold their own against the infested terrans forever basically so pushing through and going around the cliff was super unecessary. Make sure you upgrade weapons as well. The pulls are very short so you can creep a couple of steps every few seconds and never even be touched by zerglings all the while outranging any static defenses, stalkers for sniping air units, let Zeratul be a ninja and grats on your achievement.