To random lvl 37:

High ground, mejoberries are among the best, narcs to use are bio toxin (around 250+ or so, depending on the level, to get just kill the jellyfish) crossbow is alright, but tranq dart would be better. Go for the head, check hp always with a spyglass, then let it recover a bit if its health is too low to prevent you from accidentally killing it. Make sure the high ground you’re on is a CLIFF facing big rocks (this thing can walk over rocks so watch out for that also can push trees out of the way, dunno if that is a glitch but whatever). Always have a flyer at the ready, ptera is good. Taming pen is a bit hard because this bastard can damage stone with its beak attack, which can also give you torpor if it hits you. Also equip a shield, just in case. Saved my ass from lvl 130+ theris in case a hunt went wrong. Best armor to use is flak, no more no less if you wanna fight this guy, tho it can melt flak and also pierce straight through that. Pissing it off then climbing to a nearby rock a sarco can climb on spells instant death for you. Killing this as a lvl 37 is impossible without a good sword and shield at the ready. Spino also takes good care of killing this bastard. One mark for a therizinosaur is if there’s too many herbivores in the area that should normally be filled with raptors or terror birds. You’re gonna need a ton of tranq arrows to knock it out though, with a certain chance of death.

-from a mobile player, RedBlade426