Placaris = placaveris. Yes, these “syncopated” or “contracted” forms are quite common, especially in poetry where they’re metrically convenient. The v disappears and takes the following vowel along with it (except in certain 4th conjugation forms, e.g. audi(v)erunt). So you find it in the perfect paradigm (perf., pluperf., fut.perf.) of all 1st-conjugation verbs, a few 2nd-conj. ones (those that don’t go to –ui like monui, and others), and 4th-conj. ones (subject to above exception). 3rd-conj. ones (e.g. feci, scripsi) of course don’t have the v in the first place, so they have just the one form.
—This is probably more detail than you want for now (and it’s actually a bit more complicated than that). Just watch out for the shortened forms without –v-. The vowel before the ending will always be long (like the vowel before the –v- in the longer forms). Rule of thumb: if it looks funny, try the longer form with –v-.
As for the conditional: where English says
“If you do X, Y will happen,”
superlogical Latin says
“If you will have done X, Y will happen."
(For X will have preceded Y.)
It’s very common, and as you say, something else to look out for.
EDIT. Contrast this with “If you are doing X, Y will happen.” “If you are doing X” will be present.
E.g. “If you’re meaning to eat the lot yourself, (there’ll be none left for me.)” Si totum in animo habes ipse comesse, (mihi nil restabit).