You must load the draw package first.

load(draw)$

Generalized Monkey Saddle...
Let n be the desired number of tails (n=1 for the standard monkey saddle)

Monkey saddle - Mesh

n: 2$   /* n = number of tails */
m: n+2$
draw3d( surface_hide = true, color = blue, xu_grid = 35, yv_grid = 35,
axis_3d = false, xtics = none, ytics = none, ztics = none,
parametric_surface( u, v, realpart((u+%i*v)^m), u,-1,1, v,-1,1 ) )$

Monkey saddle - Surface with mesh

n: 3$   /* n = number of tails */
m: n+2$
draw3d( user_preamble  = "set pm3d at s depthorder",
colorbox = false, axis_3d = false, xtics = none, ytics = none, ztics = none,
parametric_surface( u, v, realpart((u+%i*v)^m), u,-1,1, v,-1,1 ) )$