Faster firing magic does huge damage to most Bloon types.
Arcane Spike is the fourth upgrade of Path 1 for the Wizard Monkey in BTD6. It allows the Wizard's magic bolts to deal 16 damage to MOAB-class Bloons, deal 5 damage to standard bloons, and allows the tower to pop Lead Bloons. Arcane Spike also attacks twice as fast as Arcane Mastery (every 0.275s instead of 0.55s).
Arcane Spike excels at dealing high damage to MOAB-class bloons. It becomes an effective option at handling mid-game bloons with its effective cleanup and can easily break apart multiple groups of MOAB-class quite accurately. Arcane Spike struggles versus grouped bloons, but MOAR Glaives can be paired to handle regular bloons prior to Round 81, and 0-1-2 Ice Monkeys from Round 81+ versus Super Ceramics. Pairing with Alchemist buffs, specifically with Berserker Brew or Stronger Stimulant, can reliably improve its overall performance throughout all stages of the game.
For late-game, it is good at handling MOABs and DDTs. Pairing with the main DPS towers plus support such as MOAB Glue and MOAB Press can give Arcane Spike an easier time handling groups of weaker blimps. It can also handle smaller groups of Super Ceramics adequately, although it benefits from support by the stalling power of 0-1-2 Ice Monkeys.
A 4-0-2 Arcane Spike is generally more effective than the 4-2-0 Arcane Spike because the Arcane Spike bolts have relatively low pierce, so adding Intense Magic will significantly increase the pierce of the bolts from 7 to 12. In this way, the Intense Magic upgrade is usually better than adding new weapons that don't buff the original energy bolt.
The Wall of Fire is a decent choice for additional cleanup, but it wastes the damage potential of each Arcane Spike bolt, as well as the fact that the Walls of Fire from an Arcane Spike are no stronger than a lower-tier Wizard with the Wall of Fire upgrade.
Arcane Spike is fast enough to become maximized by Stronger Stimulant without simultaneously being too fast enough to consume all of the strong brew before the duration period ends. This is because it shoots every ~0.275s by default, compared to 40 shots for the whole 5-second duration that the strong brew would need either of to wear out.
Having a Stronger Stimulant Alchemist nearby a couple of 4-0-2 Arcane Spikes can wipe out Round 95 with relative ease.
Sometimes having multiple 4-0-2 Arcane Spikes is better than a single Archmage, as they synergize better with Stronger Stimulant, deal decent overall damage and cleanup, and does not rely on saving up a significant portion of money. However, Archmage comes with the benefit of being a singular tower with greatly increased attack speed and damage, which allows it to perform far better than multiple 4-0-2 Arcane Spikes when paired with Overclock.
A 4-0-1+ Arcane Spike can solo a Fortified BFB on Logs and possibly Cubism. It can solo a regular BFB on nearly all beginner maps as well.
On Hard, a 4-x-x Arcane Spike bought by Round 40 consumes a huge portion of the money budget without farming. If possible, farm early-game so you can afford Arcane Spike by Round 40 in time to pop the MOAB easily.
Arcane Spike is slightly stronger than it was when it was first released, mainly because of pierce buffs. It got a small price nerf, but it's not a very significant nerf.
Arcane Spike bolt has more pierce, from Arcane Mastery buff (2 → 6).
Arcane Spike price increased ($10,000 → $10,900).
Arcane Spike bolt has more pierce (6 → 7, from base Wizard buff).
Description has been updated to Magic does huge damage to most bloon types.
Description has been updated to "Faster firing magic does huge damage to most bloon types".
Arcane Spike in the upgrades menu
Arcane Spike upgrade icon in upgrades menu
Arcane Spike artwork and icons
Arcane Spike with Monkey Sense, as viewed from the back
Arcane Spike with Intense Magic shooting bolts, circling around an area
Crosspathing in BTD6 (top path 2, bottom path 3)
Arcane Spike description in Version 14.0 and later
In the upgrade artwork it shows the wizard holding the staff in its right hand but the actual tower holds it in the left hand.
The upgrade icon is visually similar to the Soul Spear spell from the Dark Souls series.
Before Version 14.0, the description for Arcane Spike was "Magic does extra damage to MOAB-class bloons", but has been changed to "Magic does huge damage to most bloon types". This was possibly done to mention the fact that the Arcane Spike's magical bolts deal increased damage to almost all bloon types including Lead Bloons, but still not any to Purple Bloons (which are immune to magic).
After Version 18.0, the description was changed from "Magic does huge damage to most Bloon types." to "Faster firing magic does [...]".