SickSense

Jestrix if you read Hidden Strings carefully you will notice that when you Cipher Hidden Strings on to a creature you control, as long as you do damage to a player you may "CAST" a copy of the encoded card without paying it's mana cost.

Thus this means that say the player with the agent of fates casts hidden strings and the defending players has two blockers up. The player playing hidden Strings can "Untap" his agent of fates to trigger his heroic, then the player will have to choose to sacrifice one of his blocking creatures, then the player playing Hidden Strings will tap the ONLY other blocking creature to allow his Agent of Fates Ciphered with Hidden String to swing in for free. Once combat damage is dealt to the player, Hidden Strings Cipher ability kicks in and then the player playing Hidden Strings can then "CAST" hidden strings again with no mana cost. So in this since he would "Untap" his agent of fates, to thus remove the last blocker, and then if he wants Untap a mana of his choice since all creatures are off the board, and thus maybe freeing up mana to play something else on the board if needed.

I actually run hidden strings in my White/Blue Heroic deck and get some nasty combos on either Fabled Hero or Battlewise Hoppolite.