\documentclass{report}
\usepackage[a4paper, margin=0.75in]{geometry}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{longtable, etoolbox, tabularx, amsmath, booktabs, titlesec, makeidx, enumitem}

\makeindex

\newcommand{\attr}[1]{#1\index{Attributes!#1}}       % Attributes
\newcommand{\wpn}[1]{#1\index{Weapons!#1}}          % Weapons
\newcommand{\monster}[1]{#1\index{Monsters!#1}}     % Monsters
\newcommand{\spell}[1]{#1\index{Spells/Abilities!#1}} % Spells/Abilities
\newcommand{\eq}[1]{#1\index{Equipment!#1}}         % Equipment
\newcommand{\kw}[1]{#1\index{#1}}    

\AtBeginEnvironment{tabularx}{\footnotesize}
\AtBeginEnvironment{longtable}{\footnotesize}

% Preventing default chapters and making them look like 1: XYZ
\titleformat{\chapter}[hang]
  {\normalfont\huge\bfseries}
  {\thechapter:}{1em}{}
\titlespacing*{\chapter}{0pt}{-10pt}{*3}

\begin{document}
\input{components/front}

\twocolumn

\include{chapters/intro}
\include{chapters/combat}
\include{chapters/exploration}
\include{chapters/magic}
\include{campains/greyhaven}
\chapter{Character Sheet}
\input{components/sheet}


\clearpage
\renewcommand{\indexname}{Keyword List}
\printindex

\end{document}