To estimate S&P's credit trend for NATURGY ENERGY GROUP SA from 2021 to 2022, we will calculate the Adjusted EBITDA, FFO, and Adjusted Debt for both years based on the provided financial information and standard S&P guidelines for utilities. 

**Step 1: Identify the Industry**
NATURGY ENERGY GROUP SA operates in the Regulated Utilities / Unregulated Power and Gas sector. We will apply the baseline S&P standard formulas while ensuring relevant components (such as operating leases) are accurately included.

**Step 2: Estimate 2021 Adjusted EBITDA**
We start with the reported EBITDA.
- Reported EBITDA (Beneficio Bruto De Explotacion): EUR 3,529 million
- **2021 Adjusted EBITDA = EUR 3,529 million**

**Step 3: Estimate 2021 FFO (Funds From Operations)**
FFO = Adjusted EBITDA - Cash Interest Paid - Cash Taxes Paid
- Cash Interest Paid: EUR 488 million
- Cash Taxes Paid: EUR 864 million
- **2021 FFO** = 3,529 - 488 - 864 = **EUR 2,177 million**

**Step 4: Estimate 2021 Adjusted Debt**
We include long-term and short-term financial liabilities (which already incorporate lease liabilities) and subtract eligible cash.
- Noncurrent Financial Liabilities: EUR 15,114 million
- Current Financial Liabilities: EUR 1,698 million
- Total Debt: EUR 16,812 million
- Cash and Cash Equivalents: EUR 3,965 million
- **2021 Adjusted Debt** = 16,812 - 3,965 = **EUR 12,847 million**

**Step 5 & 6: 2021 Credit Metrics**
- **Adjusted Debt / Adjusted EBITDA:** 12,847 / 3,529 = **3.64x**
- **FFO / Adjusted Debt:** 2,177 / 12,847 = **0.169 (16.9%)**

**Step 7: Estimate 2022 Adjusted EBITDA**
- Reported EBITDA: EUR 4,954 million
- **2022 Adjusted EBITDA = EUR 4,954 million**

**Step 8: Estimate 2022 FFO**
- Cash Interest Paid: EUR 520 million
- Cash Taxes Paid: EUR 762 million
- **2022 FFO** = 4,954 - 520 - 762 = **EUR 3,672 million**

**Step 9: Estimate 2022 Adjusted Debt**
- Noncurrent Financial Liabilities: EUR 13,999 million
- Current Financial Liabilities: EUR 2,302 million
- Total Debt: EUR 16,301 million
- Cash and Cash Equivalents: EUR 3,985 million
- **2022 Adjusted Debt** = 16,301 - 3,985 = **EUR 12,316 million**

**Step 10 & 11: 2022 Credit Metrics**
- **Adjusted Debt / Adjusted EBITDA:** 12,316 / 4,954 = **2.49x**
- **FFO / Adjusted Debt:** 3,672 / 12,316 = **0.298 (29.8%)**

**Step 12: Trend Classification**
- **Signal 1 (Leverage):** 2.49x - 3.64x = **-1.15x**. Since this change is ≤ -0.2x, the signal is **Improving**.
- **Signal 2 (Cash-flow coverage):** 0.298 - 0.169 = **+0.129** (or +12.9 percentage points). Since this change is ≥ +0.03, the signal is **Improving**.

Both core ratio tests clearly indicate an enhanced credit profile during the fiscal year, characterized by a sharp growth in EBITDA driving leverage lower and greatly expanding cash-flow coverage.

<answer>Improving</answer>