I mean, if you get an extreme in Mentor Roulette, it is almost always because the sprouts don't know what an extreme is, so obviously have no idea they should prepare for it. I will always tell them that in the future it'll be smoother if they use Party Finder, and that unless they're specifically organizing a blind run it's generally good etiquette to study the fight.
(Though, keep in mind, free trial users are not allowed to create parties, whether in party finder or otherwise; queuing in directly is one of their only options.)
But once that's been detailed? It is absolutely faster for me to explain the fight in chat than make them all go watch an 8-minute video for a fight from back in ARR. Especially if I break it into bite-size chunks. For instance, to use Garuda EX as an example (since it's recent enough that I can easily remember more or less how I summarized it):
First explanation:
In the first half of the fight, there's only really two things to remember.
First, when those feathers spawn, one of them is a 'Satin Plume' instead of a 'Razor Plume'. We need to kill that one *first*; it's the thing that puts us all to sleep there.
Second, when the adds show up, the tanks will want to each take one and drag the two of them a bit apart from each other; the party can focus on Chirada first, and then go finish off Suparna.
Let's get through the adds, and then I'll cover the rest of the fight. Sound good?
Second explanation, after we'd gotten through adds cleanly:
When we get more Razor Plumes again, the special one this time will be a 'Spiny Plume'; we want to *not* kill that one.
The Spiny Plume will start stacking a debuff called 'Thermal Low' on whoever has aggro on it; if they get three stacks of Thermal Low, they explode and we all die. So we can't let one tank hold aggro the entire time if it takes too long.
Once Garuda leaves the arena again, *then* we want to kill the Spiny Plume; that'll give us a safe spot to stand in for when she comes back and does a ton of damage.
After that, there'll be some whirlwinds that appear and make chunks of the arena unsafe. The adds and the Spiny Plume will come back, and you deal with them the same way as before, just dodging whirlwinds.
(But honestly, we'll probably kill her fairly soon after the whirlwinds land, so you probably won't need to deal with that last part.)
Et voila, explanation given. The only stumbling block was that people would kill the Spiny Plume early with AoEs, but the group figured where that was going wrong pretty quickly, cleared out the Razor Plumes near the Spiny Plume individually, and then AoE'd the ones farther away down.
My typing that explanation was almost certainly far faster than trying to find a strat video for an ARR extreme and having them go watch it.