Ludovic Sylvestre struck against the run of play to give the visitors the lead just before the half-hour mark but a red card to Isaiah Osbourne left the Tangerines to hold on with 10 men for over 30 minutes.
But McGugan equalised with a penalty nine minutes from time to preserve Billy Davies' unbeaten run since returning as manager, while leaving Paul Ince's side just four points above the drop zone.
Forest recalled Adlene Guedioura, Radoslaw Majewski, Simon Cox and Darius Henderson after the quartet were left out of the 1-1 draw with Burnley while Osbourne replaced the suspended Barry Ferguson for the visitors.
The first half's pattern was set in the opening minutes with Forest controlling possession but Blackpool creating the better chances on the counter.
The Tangerines' first main threat came after nine minutes when Nathan Delfouneso cut in from the left and let fly with a curling shot from the edge of the area that came crashing back off the bar.
They took the lead with their next attack as Sylvestre grabbed his third goal of the season. The midfielder picked up the ball on the left-hand edge of the area and unleashed an effort beyond Karl Darlow's reaches into the far corner.
It was not until the 40th minute that Forest abandoned their passing game and when Greg Halford changed the rhetoric with a long ball from his own half into the area, it led to Henderson heading narrowly over.
Forest came out with greater purpose in the second period. Elliott Ward headed over from a corner before Chris Cohen forced a save from Matt Gilks with a shot from the edge of the area. And they were boosted as the visitors were reduced to 10 men for the second game in succession, as Osbourne was shown a straight red card for a late tackle on Halford.
Davies responded by bringing on McGugan, who rescued a point at Burnley, and he went close three times within five minutes of entering the fray.
His first effort, a well-struck shot from just inside the area, saw Gilks make a good save with his feet, before McGugan prodded wide from the rebound. A minute later the ball fell to him just inside the area and he fired narrowly over.
McGugan was then released down the left and put in a dangerous cross that was hooked away from danger by Kris Broadfoot. Dexter Blackstock and Billy Sharp were then both summoned from the bench, leaving Forest with four strikers on the pitch.
And the pressure told as Chris Basham fouled Cox in the area and McGugan added the equaliser - the sixth consecutive game he had found the net.
Forest pressed for a winner and were given seven minutes of stoppage time to try and find a winner, but Ince's men held on to extend their unbeaten run at the City Ground to seven matches.