Let's say SE is designing new mechanics or a twist on existing mechanics. Something to really bamboozle players as it is outside of expectations. Or, it is a rarely used mechanic that is often forgotten. It could be something new entirely too. What would you make?
Maybe I missed a particular danger- do mention them if I did.
Now, let's put a spin on them. Take your average mechanic (or multiple) and change it, replace it with something else, or create new mechanics.
I'll start with two examples.
The fail condition is not positioning the boss.
An alliance raid with 4 bosses at once for its final fight. This will mean a tank will need to double up. When a boss is felled, the tank needs to do everything in their power to drag it away far enough or else one of the bosses will consume the dead and double all of its stats (and gain a new appearance, maybe something like a fusion). the changed boss hits twice as hard and gains the mechanics of the departed. Stats double every time it eats a fallen boss. If it is felled, another boss (if close enough) might eat its corpse and gain the stats and double it. Failing to move it away after consuming the other three will make the boss go berserk and begin picking off players individually. At that point, each hit is enough to one shot a tank and then some. It stops doing anything else and chases down players and auto attacks.
Another one:
Tank buster veers upon hitting its target.
Tank busters can be line or AOE (and cone too I think). Now, what if you take the line tank buster and have it veer left or right upon hitting the tank (or unfortunate DPS)? Maybe it veers for every target it hit. In a disastrous situation it might zig zag as it hits multiple players
edit: I just remembered a discussion I had with a friend about mechanics in a general overview. What if there were mechanics that acknowledged some jobs if they were present? It may get kind of complicated if you include every job but feel free to try if you want. What would those mechanics look like?