You play a card X. What is the maximum number of cards that can be put into play as a result (including X) before you have to make a decision again?
I bid 81.
Have a big megaturn, gaining the last Band of Misfits, Golem, Herald, Copper, Silver, Curse, Estate, and having 9 copies of Throne Room in your deck. Make sure the only card in the supply costing $4 or less is Throne Room. Your hand consists of one BoM and 10 Golems. I denote any action card which doesn't have a choice by Z (if Z draws, it doesn't draw any action cards, unless I mention so).
The card X you play is BoM. You must play BoM as Throne Room (no choice) and must play Golem twice (no choice).
* The first play you find 2 Zs (no choice),
* The second play you find 2 BoMs (no choice).
** Play BoM as TR: play Golem twice, finding 2 Zs twice.
** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
*** Play BoM as TR: play Golem twice, finding 2 Zs twice.
*** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
**** Play BoM as TR: play Golem twice, finding 2 Zs twice.
**** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
***** Play BoM as TR: play Golem twice, finding 2 Zs twice.
***** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 TRs.
****** Play TR: play Golem twice, finding 2 Zs twice (drawing 10 Heralds).
****** Play TR: play Herald twice.
******* Hit and play Z.
******* Hit and play BoM: play Herald twice.
******** Hit and play Workshop: gaining the last Throne Room (no choice).
******** Hit and play TR: play Herald twice.
********* Hit and play Z.
********* Hit and play TR: play Herald twice.
********** Hit and play Z.
********** Hit and play TR: play Herald twice.
*********** Hit and play Z.
*********** Hit and play TR: play Herald twice.
************ Hit and play Z.
************ Hit and play TR: play Herald twice.
************* Hit and play Z.
************* Hit and play TR: play Herald twice.
************** Hit and play Z.
************** Hit and play TR: play Herald twice.
*************** Hit and play Z.
*************** Hit and play TR: play Herald twice.
**************** Hit and play two Zs.
Played: 10 BoMs, 10 TRs, 10 Golems, 10 Heralds, 40 Zs and Workshop, 81 total (if I can count)
An improvement: in addition to the other cards except TR, suppose you have also gained 8 Processions, one Bridge, and 3 Rogues, with the rest bought out by your opponent.
Suppose you have only bought 6 TR's, with the remaining 4 left over. And, there is only one pile left of 6 cost actions(call them G's, either Grand Market or Goons) and you've bought out Gold and Duchy.
So, the only cards left costing 6 or less are G and Throne Room.
The card X you play is BoM. You must play BoM as Throne Room (no choice) and must play Golem twice (no choice).
* The first play you find 2 Zs (no choice),
* The second play you find 2 BoMs (no choice).
** Play BoM as TR: play Golem twice, finding 2 Zs twice.
** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
*** Play BoM as TR: play Golem twice, finding 2 Zs twice.
*** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
**** Play BoM as TR: play Golem twice, finding 2 Zs twice.
**** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 BoMs.
***** Play BoM as TR: play Golem twice, finding 2 Zs twice.
***** Play BoM as TR: play Golem twice, finding first two 2 Zs, then 2 TRs.
****** Play TR: play Golem twice, finding 2 Zs twice
****** Play TR: play Herald twice.
\\Note that there's only one play of Herald here, which plays BoM. The other one will come back later
******* Hit and play BoM as TR: play Herald twice.
\\Again, another Herald starts as Procession, the second comes back later
******** Hit and play Procession: play Herald twice.
********* Hit and play TR: play Workshop twice
********** Play Workshop: gaining Throne Room (no choice).
********** Play Workshop: gaining Throne Room (no choice).
********* Hit and play Procession: play Herald twice.
********** Hit and play Workshop: gaining Throne Room (no choice).
********** Hit and play Procession: play Herald twice.
*********** Hit and play Workshop: gaining Throne Room (no choice)
//Throne Rooms are now out
*********** Hit and play Z
********** Trash Herald, gaining nothing(no choice)
********* Trash Herald, gaining nothing(no choice)
******** Trash Herald, gaining nothing(no choice)
******** //the return of the second Herald play from before
******** Hit and play Procession: play Herald twice
********* Hit and play Rogue: gaining Herald from trash(no choice)
********* Hit and play Procession: play Herald twice
********** Hit and play Rogue: gaining Herald from trash(no choice)
********** Hit and play Procession: play Herald twice
*********** Hit and play Rogue: gaining Herald from trash(no choice)
*********** Hit and play TR: play Bridge twice
************ Bridge played, cards cost 1 less
************ Bridge played, cards cost 2 less
********** Trash Herald, gaining nothing(no choice)
********* Trash Herald, gaining nothing(no choice)
******** Trash Herald, gaining nothing(no choice)
******* //the return of the first Herald play from before
******* Hit and play Procession: play Herald twice
******** Hit and play TR: play Workshop twice
********* Play Workshop, gaining G(no choice, since Throne Rooms are out)
********* Play Workshop, gaining G(no choice)
******** Hit and play Procession: play Herald twice
********* Hit and play TR: play Workshop twice
********** Play Workshop, gaining G(no choice)
********** Play Workshop, gaining G(no choice)
// out of cards in deck, shuffle 4 TR's, 3 Heralds(from Rogue), and 4 G's
********* Hit and play TR: play Herald twice
********** Hit and play TR: play Herald twice
*********** Hit and play TR: play Herald twice
************ Hit and play TR: play G twice
************ Draw G, hit and play G
*********** Draw G, hit and play G
********** No cards left, no draw and no play
******** Trash Herald, gaining nothing(no choice)
******* Trash Herald, gaining nothing(no choice)
And we're done.
I believe that's 10 TR's, 8 Processions, 10 BoM's, 5 Workshops, 3 Rogues, 10 Golems, either 10 or 14 Heralds(depending on how you count a card that was played, left play, then was played again), 31 Z's, and 4 G's, for a total of either 91 or 95.