Kargan Dragonlord

Effects that modify a leveler's power or toughness, such as the effects of Giant Growth or Glorious Anthem, will apply to it no matter when they started to take effect. The same is true for counters that change the creature's power or toughness (such as +1/+1 counters) and effects that switch its power and toughness.

The abilities a leveler grants to itself don't overwrite any other abilities it may have. In particular, they don't overwrite the creature's level up ability; it always has that.

Effects that set a leveler's power or toughness to a specific value, including the effects from a level symbol's ability, apply in timestamp order. The timestamp of each level symbol's ability is the same as the timestamp of the leveler itself, regardless of when the most recent level counter was put on it.