There are thirty-three antique coins that can be found on madhouse difficulty. All of them must be collected in a single playthrough.

If you retry or die, you must pick up all collectibles again from your most recent save.

Here is a video walkthrough of the madhouse antique coin locations, courtesy of PowerPyx:



Video Time Stamps:

Guest House:

1 - 0:05
Warning: Point of no return for Guest House

Main House:

2 - 1:50
3 - 2:05
4 - 2:21
5 - 2:38
6 - 3:05
7 - 3:18
8 - 3:30
9 - 3:56
10 - 4:21
Yard:

11 - 4:37
Old House:

12 - 5:08
13 - 5:20
14 - 5:40
15 - 6:17
16 - 6:43
17 - 7:00
Return to Main House:

18 - 7:16
19 - 7:37
Lucas's Testing Area:

20 - 8:22
21 - 8:36
22 - 8:52
23 - 9:10
24 - 9:30
Warning: Point of no return for Main House, Yard, Old House, and Lucas's Testing Area

Interior of Wrecked Ship:

25 - 9:46
26 - 10:04
27 - 10:43
28 - 11:00
29 - 11:21
30 - 11:57
31 - 12:28
Warning: Point of no return for Interior of Wrecked Ship

Before Exiting the Wrecked Ship:

32 - 13:11
Warning: Point of no return for Wrecked Ship Exit

Swamp:

33 - 13:33