A contraction of either "It would" or "That would". Used to shorten a sentence down in an easy to understand manner. Emulates Olde-English without accurately being such.
(You would use "t'was" or "'twas". People more commonly spell the word "t'was" as "'twas", but it is more accurate to say t'was according to the rules of contraction in English grammar.)
James: Wanna go hang out at the mall next week?
Jill: T'would be cool. T'would be nice if you'd give me a call later this week to remind me though!
James: Would it? T'would be very difficult, since I don't have your number!
hybrid of it and would
"t'would be good"