Can you checkmate with bishop and knight on a 9x9 bord?

Here of course it is easy. Checkmate him on i9.  The bord is bigger but there are 4 mate corners. With a white collered bishop it is of course impossible. 

Yes, but only if the four corners are the same color the bishop is on.

As for can I do it, yes, I've done it a few times before, but I'm not proficient and can let the king escape a bit.

I think so it must be possible.

1.Ke5 Ke8 2.Ke6 Kd9 3.Kd7 Ke9 4.Kc8 Ke8 5.Bd8 Kf7

6.Kd9 Kg7 7.Ke8 Kh6 8.Bh4 Kg7 9.Ke7 Kh6 10.Kf7 Kh7

11.Bi5 Ki6 12.Bf8 Kh7 13.Nh5 Ki6 14.Nf6 Ki7 15.Kg6 Ki6

16.Kg5 Ki7 17.Kh5 Kh8 18.Kh6 Ki8 19.Bg9 Kh9 20.Bi7 Ki8

21.Nd7 Kh9 22.Kh7 Ki9 23.Bh8+ Kh9 24.Nf9# 

Does the usual W-manoeuvre work on 9x9?

Or do one need to make use of Delétang's triangle?

its possible lol

Maybe this also give rise to a new chess game with a lower draw persentage and an extra knight. 

With a bishop that stand on the white collor not. Only with the bishop on the dark collor.

No there is no W -shape because all the corners are of the dark collor. So no driving from a wrong corner to the right one. A bishop on the dark collor means on all corners you can give checkmate. With a bishop of the light color all the corners are wrong!

Size doesn't matter, as long as it is finite. A knight, bishop, and king is more than sufficient to force the king to a corner. Than it's just a matter of timed manuevring

NO! not an extra knight! Add a guard for Pete's sake!

And plus you should make it 10x10 so the light squared bishop won't be REJECTED

What is a guard capable too? How does it moves I mean. 

I am not so sure of this. For example with a 10x10 bord there are dark and light corners again and I think the W-shape will fail in this case because it is not possible to prevent the king from escape to the wrong corner. I means the king can walk from wrong corner to the other wrong corner without you can hold him in the right corner as with the w - shape the with Nd7 and Bd3 methode. By a 10 x 10 bord the bord will be to big.

De W-shape in Dutch on a 10x10 bord.

1.Nh9+ Ki10 2.Bi8 Kh10 3.Bj9 Kg10  het begin van de W-shape.

4. Ng7 Kf10 de poging tot ontsnappen begint. 5.Kg6 Ke9 (normaal Kc7) 6.Nf9 Kd9

7.Bf5 deze zet verdedigt normaal a6 en belet de koning te ontsnappen.

7…Kc9 de koning ontsnapt.  8.Kf6 Kb8 9.Ke7 Kb7 10.Kd6 Kb6 11.Bd7! dit houdt de koning toch weer enigszins tegen.   Ik ben er ook niet zeker van.

It's actually an interesting question whether there might be a position on a 9x9 board that there isn't a forced mate in under 50 moves whereas there would be one on an 8x8 board. I'm guessing that it doesn't make enough of a difference, but a 10x10 would probably be a different matter.

White to move and mate in 31:

I found out that with a 10 x 10 bord ( checkers bord ) an adjusted w - shape ( in fact a triple u form ) it is still posible to checkmate black!  If you don t let win escape to a1 with your bishop and cut the king off after Ka5 white will play Kc5! and the famous w - shape will also follow on the a file! still a checkmate thus.

Several years I saw a convincing demonstration that checkmate is possible with B+N on any n x n board if n is even.  (The 50-move rule is disregarded, of course.)  Most patterns that execute this mate successfully on an 8 x 8 board have a problem when the board gets sufficiently large, due to possibility of running the defensive king around the bishop and knight and making it to the opposite "wrong corner".   However, with the aid of a chess engine, someone found a pattern that basically confined the king inside a wall, then systematically slid the wall across the board to a good corner.  So the only square boards where the mate is not possible are the n x n boards where n is odd and the bishop is the wrong color.