Arrow of Timelessness
Protips: read only if you're stuck or can't figure it out
Lightning+Explosive (max both to 3)= best crowd clearing attack in the game. Will obliterate everything given your aim is semi-decent. The reason this is the best is because on impact it, even if it doesn't kill the target, it'll obliterate it's "parts" and make it freefall to it's own doom. Not to mention the lightning arcs to nearby targets
Get the shields, they have the same effect as extending your health bar
Pierce+Homing (both lvl 3): This is the ultimate spam. Homing isn't worth it until level 3, but pierce combos well with almost anything. Once u get H3/P3, spam it. When I say spam it I mean click as rapidly as you can to get those arrows into the air. No aiming required, as long as your arrow is somewhat going toward an enemy's direction the arrow will fly toward them and decimate their parts.
Use Pierce+Homing spam to accumulate 20 arrows on screen at once (it's possible just keep spamming). Also the pierce/homing can kill the final boss in under 20 seconds. The arrows will pass through the boss hitting him multiple times and your spam will accumulate arrows in the air while the boss is teleporting.