Invasion Plans magic Master Warcraft rules combat attacing blockers

[Mint]

if attacking player controls a invasion plans

and defending player casts Master Warcraft

what happens?

[Arix]

The defending player, the one who cast Master Warcraft, chooses how to block. All of his creatures that are able to block, must.

[Mint]

why?

[Arix]

Both Invasion Plans and Master Warcraft create continuous effects that modify the rules of the game. Since they clash with each other, you apply them in timestamp order. Master Warcraft has the latest timestamp, so that's the one which applies.

[Mint]

if the attacking player controls a Windborn Muse, can defending player force him to pay for attackers?

[Arix]

No.