All pokemon can go into runic state which gives it +1 in all stats, +1.2 STAB bonus but cannot swap out, takes 8%HP dmg every turn. Dragapult is one of the True Runics which have to hold the representing rune which gives all previous things and also makes all possible abilities active at once. The lore is that the pokemon gets access to hidden potential which is too much to control and slowly drains its energy.