Find all triplets of nonnegative integers $(x,y,z)$ and $x\leq y$ such that 
$x^2+y^2=3 \cdot 2016^z+77$
1. **Initial Analysis:**
   We start with the equation \(x^2 + y^2 = 3 \cdot 2016^z + 77\). We need to find all nonnegative integer triplets \((x, y, z)\) such that \(x \leq y\).

2. **Non-zero Condition:**
   Clearly, \(x, y \neq 0\). If either \(x\) or \(y\) were zero, then we would have:
   \[
   3 \cdot 2016^z + 77 \equiv 2 \pmod{3}
   \]
   This would imply \(x^2 \equiv 2 \pmod{3}\) or \(y^2 \equiv 2 \pmod{3}\), which is impossible since squares of integers modulo 3 can only be 0 or 1. Therefore, \(x, y \in \mathbb{Z}^+\).

3. **Case \(z = 0\):**
   If \(z = 0\), the equation simplifies to:
   \[
   x^2 + y^2 = 3 \cdot 2016^0 + 77 = 80
   \]
   We need to find pairs \((x, y)\) such that \(x^2 + y^2 = 80\) and \(x \leq y\). Checking all pairs \((x, y)\) with \(x, y \leq 8\), we find:
   \[
   (x, y) = (4, 8)
   \]
   Thus, \((x, y, z) = (4, 8, 0)\) is one solution.

4. **Case \(z \geq 1\):**
   For \(z \geq 1\), we analyze the equation modulo 7:
   \[
   3 \cdot 2016^z + 77 \equiv 0 \pmod{7}
   \]
   This implies:
   \[
   x^2 + y^2 \equiv 0 \pmod{7}
   \]
   Since \(n^2 \equiv 0, 1, 2, 4 \pmod{7}\), for \(x^2 + y^2 \equiv 0 \pmod{7}\), both \(x^2\) and \(y^2\) must be \(0 \pmod{7}\). Therefore, \(x\) and \(y\) must be divisible by 7. Let \(x = 7n\) and \(y = 7k\). Substituting these into the original equation, we get:
   \[
   49n^2 + 49k^2 = 3 \cdot 2016^z + 77
   \]
   Simplifying, we have:
   \[
   n^2 + k^2 = \frac{3 \cdot 2016^z + 77}{49}
   \]

5. **Case \(z \geq 2\):**
   For \(z \geq 2\), we check modulo 49:
   \[
   3 \cdot 2016^2 + 77 \equiv 28 \pmod{49}
   \]
   However, \(49n^2 + 49k^2 \equiv 0 \pmod{49}\), which is a contradiction. Therefore, \(z = 1\).

6. **Case \(z = 1\):**
   For \(z = 1\), the equation becomes:
   \[
   49n^2 + 49k^2 = 3 \cdot 2016 + 77 = 6125
   \]
   Simplifying, we get:
   \[
   n^2 + k^2 = 125
   \]
   Checking pairs \((n, k)\) such that \(n, k \leq 11\), we find:
   \[
   (n, k) = (2, 11) \text{ and } (5, 10)
   \]
   This implies:
   \[
   (x, y) = (14, 77) \text{ and } (35, 70)
   \]
   Therefore, \((x, y, z) = (14, 77, 1)\) and \((35, 70, 1)\) are the other solutions.

Conclusion:
\[
\boxed{(x, y, z) = (4, 8, 0), (14, 77, 1), \text{ and } (35, 70, 1)}
\]