White spindly troll encrusted with fungi which is itself symbiotically bonded to rare archean bacteria. These produce rare metals and impossible elements at a slow rate and encode them in micro-helixes inside the fungi. Like a polar bears hair has a spiral inside it that refracts infra-red. These things refract time. Troll looks kind of crazy and beautiful with weird glintings inside its fungal lumps.
Tachyon Troll starts at 1 hp. Looks all fucked up, like its just been in a fight. You have to fight it. If you don't the temporal energy released will slowly kill you until you do. Each blow restores hit points. When it reaches max it's regeneration kicks in. The troll knows all possible futures for itself and this has given it buddha-like wisdom. It doesn't hate you. It's trying to kill and eat you because this is the tao of the troll. Speaks calmly in gnomic parables while you fight it. Reassures you. Accepts death calmly when it comes. It was always fated to end this way. Maybe surviving a long fight with one gives you a new perspective on life, possible WIS bonus, free alignment change or life insight.