Think of movement not just as getting from A to B, but as a tool for Vek manipulation. Block Vek spawn points with your mechs (though they will take damage). Position mechs to create choke points. Use push abilities to move Vek into each other's attack paths, causing them to damage each other. Remember that some Vek, like the Hornet, can fly over obstacles. Always consider the next turn's Vek spawns when positioning your mechs.
