I play Magic casually, and I just got into EGS, I think I can form an informed opinion on this card.
Using him to pump your creatures, while it may seem redundant at first, can have merits depending on the card you intend to morph your guy into (I just used three different words to refer to creatures WHATS WRONG WITH ME). It can be used to bypass certain drawbacks of cards like Avatar of Discord (3 mana, 5/3 flyer, when it arrives you discard 2 or it goes boom, but morphing a thing into it bypasses this). The fact that Tedd's ability doesn't require colored mana is a big plus to this tactic, which is also very difficult to counter (Tedd himself on the other hand...). Quirky and workable, but not spectacular.
The alternative, shrinking your opponent's duderoonies? I don't think it's balanced as it can be used as incredibly cheap mass removal with one-turn wonders like Spark Elemental. They're very cheap, can deal enough damage on their own to be a viable win condition, and a deck revolving around them would only need minor alterations to accomodate Tedd. Then again, I could be overestimating the tactic, as I only play casually.