Found a instruction for a Modified 76105 UCS Hulkbuster on Bricklink with bendable legs. I built it in the LDD first to reduce most of the Gray pieces which the original MOD
LEGO 76210 Avengers Age of Ultron Hulkbuster | BrickEconomy
LEGO Set 76105-1 The Hulkbuster: Ultron Edition (2018 Super Heroes Marvel > Avengers) | Rebrickable - Build with LEGO
LEGO Super Heroes: Avengers Age of Ultron: The Hulkbuster: Ultron Edit – Brick Loot
LEGO® The Hulkbuster: Ultron Edition - MyBricks.net
LEGO 76105 Age of Ultron The Hulkbuster Ultron Edition | BrickEconomy
Sticker Sheet for Set 76105 - (38385/6224451) : Part 76105stk01 | BrickLink
LEGO 76210 Hulkbuster review | Brickset
The Hulkbuster: Ultron Edition : Set 76105-1 | BrickLink
The Hulkbuster Smash-Up : Set 76104-1 | BrickLink
LEGO Super Heroes: Avengers Age of Ultron: The Hulkbuster: Ultron Edit – Brick Loot
Set 76105-1 : The Hulkbuster: Ultron Edition [Marvel Comics] [BrickLink]
UCS Hulkbuster Mod from BrickLink Studio
The Hulkbuster: Ultron Edition : Set 76105-1 | BrickLink
Set 76105-1 : The Hulkbuster: Ultron Edition [Marvel Comics] [BrickLink]