This card is probably one of the best cards to ever be made. It has very few weaknesses, a whole bunch of strengths, and several ways to be really evil with it.
Stuffy Doll is primarily a blocker, of course. As a 0/1 creature, unless you pump him, he obviously can't attack, and his main advantage is his damage reflection, so save him to block their giant creature.
Strategies and game play:
He's a blocker. their big critter now, instead of hurting you, hurts them, so most players won't bother attacking while he's on the table. So get him out, target your biggest threat (in multiplayer) and then plan your next move, reasonably secure in the fact that they won't be attacking until they can deal with Stuffy Doll.
Don't forget, as your last opponent declares the end of their turn, before your untap phase, to tap him to deal one damage to himself. This damage, of course, is reflected back at whoever Stuffy is targeting.
Combos with other cards:
By himself: Stuffy Doll is simply a very, very good blocker. Your opponent has to calculate how much damage they'll take against how much damage will get past. Usually, most players only have one or two heavy hitters out, which means that their heavy hitter is going to end up hitting them instead, and what's left over usually won't be enough to make it worth their while.
Pariah's Shield + Stuffy Doll: Who needs blockers? Any damage done to you is reflected towards the creature Pariah's Shield is attached to. Normally, this wouldn't be very good, you'd kill off one of your creatures instead of taking the damage yourself, but now, with Stuffy Doll, any damage you take is sent back, 100%, to your opponent. This frees you up to go all out offensive, or tap your creatures for whatever purpose, because unless they have arty hate, you won't take any damage.
Skred + Stuffy Doll: This first happened to me in a multiplayer game. It's incredibly evil, because mid/late game, Skred can be a heavy hitter, but it only targets creatures. Hey, look. Stuffy Doll is a creature. Now Skred works on players! I was playing a game of Two-Headed Giant not too long ago. I had one stuffy doll out, and various assorted snow cards. My teammate was also playing a deck that ran snow/Skred. We ended up Skredding Stuffy Doll 4 times in a single turn, for a total of 4 red mana, and doing something like, 35 damage. Our opponents died.
Ways to counteract it:
Discards: Stuffy's not indestructible if he's still in your hand.
Trample: Trample blows right through Stuffy Doll, as only 1 will hit him, and the rest will carry on directly to you. If you have the Pariah/Stuffy combo up, that's not a problem, but if you don't... ouch.
Remove from Game: These sort of arty/creature hate will still work on Stuffy. He's only immune to Destruct and direct damage.
-x/-x: Stuffy will still die if he has no toughness. Anything that gives a creature -x to toughness will kill him instantly.
Very hard to get rid of. Reflects damage, and can be used in combo with spells that only deal damage to creatures.
Is only a 0/1 for 5. Granted, he's immune to a lot of things, but there are still several ways to get rid of him, and after people see that you play with him, they're going to start running heavy on those things to get rid of him.
Time Spiral was the first, and so far only, printing of Stuffy Doll.
Artwork and aesthetics:
It harkens back to some old school cards. For a long while, there was an artist that used a stuffy doll in a lot of his artwork. Vise, for example. There were just a whole bunch of cards that depicted this rag doll getting the stuffing beat out of him (pun intended) but obviously, none of this stuff ever actually got RID of the doll.
9. Very good card, has some incredible combos, and unless your opponent is specifically planning on fighting a stuffy doll, they won't be prepared to deal with him.