Mega Swampert :
•Waterfall / Liquidation -> STAB option for mega Swampert that got boosted by rain. Liquidation for that small defense drop change and waterfall for that flinch change.
•Earthquake : Reliable STAB option for mega Swampert.
•FlipTurn : Option to switch and gain momentum while dealing decent damage.
•Bulk up : Option to setup for mainly attacking stats.
•Ice Punch : for Mega Salamence / grass type pokemons.

Note : ALWAYS put mega Swampert in rain and dont Ice punch Dragapult unless you're running bulk up set. Gain advantage from the rain as much as you can and dont be afraid of dying after killing 2 or 3 kills unless its important for specific match up.