is krogstad a complete villain? what are his motivations for his actions?

Krogstad certainly looks like a villain on paper. He tries to manipulate, intimidate and threaten Nora into keeping his job at the bank. I don't think Ibsen was concerned with stereotypes. There was always something more nuanced to Krogstad that defied a simple antagonist bad guy. He wanted another shot at respectability. After forging signatures and getting fired, Krogstad wanted some redemption. Is that really so bad? Even in his worst moments he seemed to understand Nora better than her husband Torvald. At one point they both (Nora and Krogstad) brood about suicidal thoughts which is an awkwardly tender moment, "Most of us think of that at first. I did, too – but I hadn't the courage... She replies quietly, "No more had I." In the end Krogstad is redeemed "regrets and repents" his actions.