I have two minipages one above the other with [b] and [t] options set to have right baselineskip. Second minipage/varwidth is in the multicols environment and if it have more then two lines, it getting outside the textheight. What to do?
\documentclass{article}
\usepackage[paperwidth=10cm,paperheight=5cm,showframe]{geometry}
\usepackage{varwidth}
\usepackage{multicol}
\premulticols0pt
\postmulticols0pt
\columnsep0pt
\setlength{\multicolsep}{0pt}
\begin{document}
\noindent LABORE ET DOLORE
\vfill
\noindent\begin{minipage}[b]{\linewidth}
\raggedleft
LOREM IPSUM
LOREM IPSUM
\end{minipage}
\begin{multicols}{2}
\null
\vfill
\noindent DOLOR SIT
\columnbreak
\noindent\hfill\begin{varwidth}[t]{.5\textwidth}
\raggedleft
MAGNA ALIQUA
MAGNA ALIQUA
MAGNA ALIQUA
MAGNA ALIQUA
\end{varwidth}
\end{multicols}
\end{document}

Update
I change slightly @alephzero code in order to flush baseline of the tabular text to the bottom (with descenders out of textheight). I know it isn't pretty solution. But it works.
\documentclass{article}
\renewcommand{\arraystretch}{0}
\usepackage[paperwidth=10cm,paperheight=5cm,showframe]{geometry}
\newlength{\myheight}
\begin{document}
\setlength{\myheight}{\fontchardp\font`p}
\noindent LABORE ET DOLORE
\vfill
\noindent\begin{minipage}[b]{\linewidth}
\raggedleft
LOREM IPSUM
LOREM IPSUM
\end{minipage}\strut
\noindent\begin{tabular}{@{}l@{}l@{}}
\parbox[t]{0.5\linewidth}
{DOLOR SIT}
&
\parbox[b]{0.5\linewidth}
{\raggedleft
MAGNA ALIQUA
MAGNA ALIQUA
MAGNA ALIQUA
MAGNA ALIQUA\vphantom{p}}
\end{tabular}
\enlargethispage{\myheight}
\end{document}

multicolshere. If you are usingminipageenvironments, you already have control over the alignment. Why put them in amulticolsenvironment as well? – cfr Apr 30 '15 at 23:34minipageinsidemulticolsbecause I need to have correct baselineskip between right-sided minipages and bottom aligning of left-sided text (DOLOR SIT) at the same time. – web-stranger Apr 30 '15 at 23:46