TJMP will also jump if T contains a word, since words are "not equal to 0".

TJMP will jump when T is ANYTHING OTHER THAN 0
Not just when it's greater than 0.
For example T = -1 will cause a jump.

For peaslee:
Digits that aren't 1, 2, 3 or 4, when used as a mask in a SWIZ command, will insert a zero. Great for those [rare] times when you need to null out a specific digit or insert some padding.

@REP 4
LINK @{803,2}
@END

Would be a better way to do what Gargish said

I believe MARK does count towards size / line count.

Semicolons work as notes.
;HELLO
is the same as
NOTE HELLO

Adding to weev's macro comment: Macro counter substitution

@REP 4
LINK 80@{3,2}
@END

expands to

LINK 803
LINK 805
LINK 807
LINK 809

that is, first number in braces is the initial value, the second is the step count, and since it is just a text replacement you can string it together with other text.

Using

@REP N
thing to repeat
@END

is a hidden convenience for repeating something a fixed number of times - I don't think you can use a register in place of N.

@REP 5
copy m x
@END

expands at runtime to

copy m x
copy m x
copy m x
copy m x
copy m x

You can also alt-click on a line to run the program to that point, like a breakpoint. Not sure if there are any other hidden gems like this.

You can use a one-digit mask with SWIZ.

SWIZ 1234 2 X (copies 3 into X)

MARK adds to size, but not to cycles. Rather strange, since one would presume it's a precompiled address, however EXAPUNKS doesn't support absolute or relative branching so it's its own goofy thing.