Complex sentence: Then the Smurf of Christmas Future, who appears as Hefty Smurf, shows Grouchy his future, telling him that if he does not change his ways, all of the Smurfs will wander into the forest and get captured by Gargamel.
Split into simpler sentences: Then the Smurf of Christmas Future, who appears as Hefty Smurf, shows Grouchy his future. Hefty tells him that if he does not change his ways, all of the Smurfs will wander into the forest and get captured by Gargamel.