You backpedal until you're out of its range. Lucky it's branches can't reach across the whole courtyard. That gives you a little breathing room to think and plan a response.
You can't fight it yourself, that much is obvious. Your hooves are sore enough already at the thought of trying to punch and kick a tree into submission.
One mare can't fight a tree alone... but six might make a difference.
You pull out your Wand of Summoning and... wonder how the heck you're supposed to use it. It's not like Twilight's magic, she just... lights her horn and stuff happens. Maybe if you stick the wand to your forehead...
No, that's ridiculous. You give it a shake and as you do, feel an odd pull from it to the left. It's a good a sign as any. You move the wand left till you feel it start to pull up. One direction at a time, it guides your hooves through a complex series of motions, loops and swipes and graceful arcs, at one point it even directs you to spin around. All the while the star crystal glows brighter and brighter.
Finally, the wand guides you to slam it into the ground, the impact scattering a burst of yellow sparkles. Where they land, the ground starts to crack and bulge, soon punctured by rising hooves. Five zombies pull themselves up and out of the dirt to stand at attention in loose formation around you. But these aren't the same faceless generic ponies you faced before. No, these ones wear the faces of ponies you know.
Bon Bon and Carrot Top. Sweetie Belle and Cheerilee. Even Soarin from the Wonderbolts. They're all strongly green and missing a few small parts like ears or horns or patches of fur, but they all look much less grossly rotting compared to the ones you fought before. Different enough that you can easily remember that they're magical creations and not the real thing.
"Alright team! We've got an angry tree on our hooves and I don't know about you, but I don't feel like getting turned into fertilizer." Zombie Sweetie Belle raises her hoof, but quickly puts it back down looking sheepish. "I'm the squishiest one here, so I need you all to keep that thing distracted as much as you can while I look for a weak point. Got it?"
Your team nods in understanding and agreement. At least you hope they are. Hard to tell just how functioning their brains are. They split up and charge into the fray from five separate directions. Zom Bon and Carrotten Top take to the left, Zombelle and Zombilee the right, while Zoarin flies in from above. As they enter the tree's range, the branches converge on their positions, reducing the number wildly thrashing through the air by a huge amount.
You take to the sky, thankful for the high ceiling, and start circling the tree. It has to have a weak point somewhere. All giant monsters do, whether it's a big glowing eyeball or old wound they try to armor over. All you have to do is find it, then the battle's half won. You give a glance to your newfound companions. Zom Bon and Carrotten Top are working together well, coordinating their movements so branches end up smacking into each other and getting their smaller branches tangled. Zombelle almost looks like she's having fun, hopping over low swinging blows like it's some kind of extreme jump rope with Zombilee bucking back the bigger threats heedless of the damage it's doing to her legs. Zoarin has taken a couple of hits and lost a foreleg, but his aerial ballet is tangling a lot of of the smaller whippy branches and keeping them off you.
They're doing well for now, but with enough small damage even they'll fall sooner rather than later, so you need to be quick.
You make another pass over the top of the tree, looking intently for any flaw or weakness. A glint of light catches your eye. There! Stabbed deep into the upper boughs of the trunk there's glint of metal.
"Peel it open!" you cry, hoping whatever magic makes them obey will also convey your plan. "I'm going in!" You turn your arc into a dive as Zoarin drags the upper branches' attention to the side. Zombilee and Zom Bon throw their partners into the air, coaxing apart the upper branches until the top looks like a mane of hair parted by a comb, leaving your target exposed.
You pump your wings, pouring on the speed, ignoring the few skinny branches that whip at your legs and barrel. As you approach, you can finally make out your target. It's a sword, made of a scratched black metal, half sticking out of a weird growth on the very top of the tree.
Indecision suddenly strikes you. Should you plunge the sword in deeper or pull it out?