Predecessor Builds > Gideon > Powerful and slowing
With this build you'll finish with 410 magical power, tenacity ( anti-CC of 45% ), decent ability haste ( 25 plus timewarp reduces cooldown by 1s) and up to 30% magical pen ( with Caustica ), with the added bonus of slowing your enemies - admittedly the slow is less helpful end-game but Dreambinder also packs plenty of magical power and tenacity so worth it.
NB Make sure you start with one or maybe two mana regens, so you can keep mana high, then swap them out when you get to Caustica as you'll have more passively anyway and caustica will give you insane mana regen
You can consider a different item to Tainted Sceptre ( eg Megacosm is good combined with world breaker ), but it's useful for it's anti-heal and now also extra magical pen for those tanks and assassins.
End game you can push on with some safety from magical and physical armour and tenacity combined with your shield can keep you fairly safe or a decent chance of not getting stunned and kill the game off in those team fights.