This sequence appears to follow a multiplicative pattern. Let's analyze it step by step:

1. The first number is 2.
2. The second number is 6, which is $2 \times 3 = 6$.
3. We are missing the third number (denote it by $?$).
4. The fourth number is 30, which is $6 \times 5 = 30$.
5. The fifth number is -270, which is $30 \times (-9) = -270$.

It seems that the pattern involves multiplying by increasing odd integers (3, 5, -9). So, to find the missing number, we can multiply the second number (6) by the next odd integer, which would be 1:

$6 \times 1 = 6$

Thus, the sequence should be:

$2, 6, 6, 30, -270$

The missing number is 6.

Would you like a more detailed explanation or have any questions?

Here are five related questions:

1. What are the next two terms in the sequence if the pattern continues?
2. Can you identify another sequence with a similar alternating multiplication pattern?
3. How would the sequence change if we multiplied by even numbers instead of odd ones?
4. What is the general term formula for a sequence that follows a multiplicative pattern?
5. Can you create a sequence using addition instead of multiplication?

Tip: When working with sequences, check for both arithmetic (addition/subtraction) and geometric (multiplication/division) patterns.