press space to shoot succeeding to kill waves gives the most points, so try to save up. reaching 20 points gives you a furnace, 30 for a iron sword, 75 for a diamond sword, and TNT on 200. (the final boss has epic music, and gives <><> points)
thanks to mojang and nintendo (+whoever made invaders) here's a list of those bad mobs you will battle: zombies and skeletons do nothing but walk. slimes get smaller till they are gone. creepers go boom and protect the enemies beside them. ghasts shoot fireballs to try and touch the edge. enderman teleport vertically. blazes move horizontally. THE BOSS does... shulkers are fast blazes silverfish have camo the few times you see them enderghasts (0.0) are the combined power of enderman, ghasts, and camo purplur (chorus fruit) grows more of itself ships do a the final boss does... basically: slime=become smaller creeper=boom ghast=blast shulker/blaze=move horizontal end=vertical teleportation (0.0) I will add a wither boss later (0.0)