I have one time series which is represented by a black line and one which is represented by a red curve. Then I have single points which have the pch symbol of 8 in R. These are
Try this. You set lty to display only first two lines, and pch to display only the last point.
plot(1:10, rnorm(10) * 1:10)
legend("bottomleft", legend = c("entry1", "entry2", "something cpl different"), bty = "n",
lwd = 2, cex = 1.2, col = c("black", "blue", "red"), lty = c(1, 1, NA), pch = c(NA, NA, 8))