Here's a guide by robbagus on how to kill a Teostra in Monster Hunter 4 Ultimate easily.
Robbagus been hunting lots of Teostra lately and his pretty confident of my Teostra-killing tactics, so He figured why not make a guide, and here it is.
To add on, if you’re doing the timer, take note that these events will force Teostra to return to normal state, which resets the timer until it initiate rage mode again. Cutting of tail, breaking of horn and a successful mount.
Combo-locking – One of the main reason why people struggles with Teostra. Teostra is ridiculously good at combo-locking. The deadliest combo is when he charges at you, making you fall infront of him, then combo with a perfectly timed nova (not super) that will hit you the moment you get up. Also there the side-swipe that leave blast-gas behind. If the side-swipe makes you roll along the floor, you should be fine. But if it only makes you trip, you will be combo-locked by the detonation of the gas spawned by the swipe, convieniently right at where you trip. Unless it’s the combo above which trips you, you should generally be fine countering the other combos. Don’t get up after you roll along the floor. When you get hit, be patient and judge Teostra’s next movement, if he is going for a nova (he usually would), stay on the floor, don’t move your D-Stick. Your invincibility period will continue and you will avoid the nova, that simple.
Note, you should always prepare for the incoming combos when Teostra hits you with a physical move, mainly side-swipe and charge. On the other hand, you will mostly be safe if he hits you with a range/blast attack as he usually does this roar whenever he detonates blast-gases which gives you the chance to run.
General Tactic – General rule while fighting Teostra, keep circling around it, wait for it to initiate a move, and aim for the backlegs. The weakest point of Teostra is it’s head, followed by it’s backlegs. In fact, there’s not much difference except you will be a lot safer hanging around it’s backlegs. The main weakness of Teostra is it’s reeeaaally long attack animations. If you are in the right position when it initiates an attack, a GS user can easily pull off a level 3 charge. DS users can sheath attack, goes into demon mode and finish of a Demon dance, Long Sword can do a finisher combo, etc etc, you get the gist. Take your time, learn it’s behaviour and you can almost be unscathed for the whole game.
EDIT: KO-ing Teostra will also knock it out off enraged mode.
Credits: Guide by robbagus