Whisk together reserved pineapple juice, sugar, cornstarch, lemon juice and salt until smooth.
Place mixture into a small saucepan over medium heat.
Bring to a boil stirring continually, then cook 3 minutes or until sugar dissolves.
Remove from heat.
Beat eggs slightly with a fork and add 2 Tbsp of the hot syrup mix. Mix quickly to combine, then pour it into the remaining hot syrup.
Place the pan over low heat and bring to a gentle boil.
Cook for 2 minutes, stirring continually.
Remove from heat and transfer to a bowl. Allow to cool to room temperature.
Gently fold together the pineapple chunks, bananas, grapes, oranges, cherries and marshmallows.
Drizzle the cooled syrup over the fruit and toss to combine.