Then there is Eovaldi, with his 4.10 regular season ERA, but a 2.90 in 50 postseason innings
In a somewhat unscientific survey, I went looking for other outliers over the past few decades. Outliers are an ERA differential of more than one run between career regular and postseason ERAs, and discounting small sample sizes (fewer than 50 postseason innings pitched).
The Good:
Stephen Strasburg: 3.24 career ERA, 1.46 postseason ERA in 55 1/3 innings (1.78)
Colby Lewis: 4.70 career ERA, 3.11 postseason ERA in 55 innings (1.59)
Matt Cain: 3.68 career ERA, 2.10 postseason ERA in 51 1/3 innings (1.58)
Orlando Hernández: 4.13 career ERA, 2.55 postseason ERA in 106 innings (1.58)
Madison Bumgarner: 3.47 career ERA, 2.11 postseason ERA in 102 1/3 innings (1.36)
Tim Lincecum: 3.74 career ERA, 2.40 postseason ERA in 56 1/3 innings (1.34)
Curt Schilling: 3.46 career ERA, 2.23 in 133 1/3 innings (1.23)
Barry Zito: 4.04 career ERA, 2.83 postseason ERA in 60 1/3 innings (1.21)
Jon Lester: 3.66 career ERA, 2.51 postseason ERA in 154 innings (1.15)
Aníbal Sánchez: 4.06 career ERA, 2.93 postseason ERA in 61 1/3 innings (1.13)
The Bad:
David Price: 3.32 career ERA, 4.62 postseason ERA in 99 1/3 innings (1.30)
Max Fried: 3.03 career ERA, 4.43 postseason ERA in 61 innings (1.40)
James Shields: 4.01 career ERA, 5.46 postseason ERA in 59 1/3 innings (1.45)
C.J. Wilson: 3.74 career ERA, 5.26 postseason ERA in 53 innings (1.52)
Lance Lynn: 3.74 career ERA, 5.28 postseason ERA in 58 innings (1.54)
Clayton Kershaw: 2.48 career ERA, 4.49 postseason ERA in 194 1/3 innings (2.01)
Tim Wakefield: 4.41 career ERA, 6.75 postseason ERA in 72 innings (2.34)
If you drop the threshold to 40 innings, you could also add these guys to the "bad" list.
- Johnny Cueto: 3.50 career ERA, 4.54 postseason ERA in 41 2/3 innings (1.04)
- Scott Kazmir: 4.02 career ERA, 5.18 postseason ERA in 41 2/3 innings (1.16)
- Luis Severino: 3.79 career ERA, 5.15 postseason ERA in 43 2/3 innings (1.36)
- Tyler Glasnow: 3.89 career ERA, 5.72 postseason ERA in 45 2/3 innings (1.83)
- A.J. Burnett: 3.99 career ERA, 6.37 postseason ERA in 41 innings (2.38)