To beat Candy Crush Level 16255, follow these detailed steps:

1. **Understand the Requirements**
– **Objective**: Collect all the Rainbow candies, clear all 78 jellies, and reach 88,000 points to complete the level.
– **Moves**: You have only 21 moves to achieve this.
– **Rainbow Candies**: You need to collect 7 Rainbow candies.

2. **Strategic Play**
1. **Start from the Bottom**:
– Begin by playing from the bottom of the board. This helps in creating opportunities to make matches and clear jellies from the bottom up.

2. **Play Near Blockers**:
– Try to play near blockers (locked candies) as much as possible. This increases the chances of creating matches that can clear jellies and other blockers.

3. **Use Striped Candies Strategically**:
– Use striped candies to break multiple jellies at once. This is crucial for clearing all 78 jellies within the limited number of moves.

4. **Focus on Jelly Clearing**:
– Prioritize clearing jellies over collecting Rainbow candies initially. Clearing jellies will create space and make it easier to collect Rainbow candies later.

5. **Collect Rainbow Candies**:
– Once you have cleared some jellies, focus on collecting Rainbow candies. Try to create matches that include Rainbow candies whenever possible.

6. **Manage Your Moves Efficiently**:
– Make sure you use your moves wisely. Avoid making unnecessary moves that don’t contribute to clearing jellies or collecting Rainbow candies.

7. **Use Boosters Judiciously**:
– If you have boosters available, use them strategically to help clear jellies and collect Rainbow candies.

3. **Additional Tips**
– **Shuffle the Board**:
– If possible, try to shuffle the board by making matches that move candies around. This can sometimes create new opportunities for matches.

– **Lucky Board**:
– Sometimes, you might get a lucky board layout that makes it easier to clear jellies and collect Rainbow candies. Take advantage of such opportunities if they arise.

By following these steps and strategies, you should be able to beat Candy Crush Level 16255 efficiently and effectively within the given number of moves.