to kill rathalos first get a pitfall trap and shock trap secend get some flash bomb and
paint boll third upgrade your sword into devil slicer then you can kill rathalos easily

1.stun him with flashbomb
2.put 2L.g barral bombs next to him
3.put 1 small barral bomb next to it and run away if not dead reapit it

first of all you can only hold up to three lg bombs at a quest but it is a good idea it
could also help by using demondrugs and armorskin
demon drugs = catalyst + powerseed
armorskin = catalyst + armorseed
catalyst = bitterbug + honey