I would theorymon this set
Togetic @ Leftovers
252HP/4Def/252SpD
Calm
Serene Grace
-Twave
-Tri Attack
-Roost / Nasty Plot
-Light Screen / Baton Pass
Roost/Light screen present a special defense/para spreading set. Come in and check certain special threats, setting up light screen to help itself and (less so) others, to help others switch to light clay. After a Twave it will be outspeeding some pokes so roost will become effective changing its typing. Its totally walled by things like rhyperior, steelix, chansey and things that substitute before togetic can Twave (togetic should twave first to catch anything on the switch).
Should check Venusaur if something has been slept already (grass, ground should do much). Porygon might have too much power for it, it cant hurt mismagius but milotic may find it difficult if roosting before the ice beam.
Nasty Plot/ Baton pass looks a better option to me. if the Twave is successful it will near certainly get off a Nasty Plot, it can then Tri Attack or pass. Imagine an alakazam, a moltres, a raikou with a Nasty Plot or, as i prefer, an Octillery. Togetic is against Ambipom in the Nasty Passing category. Its advantage is that it can use the boosts itself better, it has better (special) defense, it has twave and it has surprise factor. It does miss taunt though.