With Teddy dead at the very beginning of this mystery, apparently as the villain, being played by Pantoliano only reinforces this concept suggesting that at the beginning that Leonard was absolutely right, and there is not anything complex about Teddy at all. The truth though is Teddy is a far more complex character and it is surprising to see Pantoliano's portrayal which slowly reveals more to Teddy with every scene we see in reverse. In the first, last, scene of Teddy though Pantoliano is fitting his usual role of the somewhat obnoxious, somewhat overbearing personality. It is interesting though as the film reveals that this is not just a standard Pantoliano character.
Teddy keeps showing up for some reason, either at Leonard's beckon call or just showing up to see him for some reason. Pontaliano is good in suggesting that Teddy seems to know more then he claims toward Leonard. Pantoliano plays Teddy in an interesting way as he sort of plays Leonard while protecting him as well. Pantoliano isn't warm but there is a certain concern he conveys in Teddy as he constantly seems to keep helping him and offering him advice. At the same time Pantoliano gives the sense of a trick he is playing as Teddy so often changes his greeting method to Leonard, sometime acting like an old friend, and at other times a bit of a stranger.
Pantoliano's performance is a good one because his way of being the the untrustworthy friend properly indicates the truth behind Teddy that is revealed in the end. The truth being that he has manipulated Leonard in a despicable way, but that was after and still being the one person who seems to care for him. Pantoliano is very strong in the last scene frankly opening up completely with Teddy revealing the strange mix of mostly despicable but just slightly honorable nature of Teddy. He is not a villain exactly, and certainly not the villain one would assume he was at the beginning, as Pantoliano brings the complexity of Teddy to life. Pantoliano does falter a bit with a bit too much of his usual overacting, nevertheless he does make Teddy a compelling facet of this great film.