Umbra is the final boss of Kingdom Rush: Frontiers.
Umbra is not made of shadows, shadows are made of Umbra...
At the beginning of the stage, Umbra is encased in a huge crystal on a high plateau, with Lord Malagar attempting to free him. Neither Umbra nor Lord Malagar can be attacked in this state. After wave 15, Umbra is freed, kills Lord Malagar and attacks you.
Umbra does not move towards the exits (he summons Shade Elementals for this purpose), instead, it only teleports between the main path and the plateau, where it is invulnerable to all attacks, including ones with unlimited range.
After its health is depleted, Umbra splits into eight Shreds of Darkness, which will move toward the plateau in an attempt to reform Umbra. They can be blocked, however whenever one reaches the plateau or two of them are killed, all will hurry up to the plateau to form Umbra again. Umbra's health when reformed depends on how many Shreds of Darkness remain when it reforms. Umbra will also start destroying towers from the first reform. Its attacks appear as blue lightning shooting out of its eyes.
Umbra must be defeated four times to be fully killed.
- Before wave 15 starts, stop buying towers and upgrades unless they directly affect Umbra. You should be fine with the current setup, having survived 14 waves earlier. The gold you save up during wave 15 should reach 1000 or more. If it doesn't, sell a few unimportant towers after Umbra reforms the first time; you need 1000-2000 gold rebuild the towers Umbra will destroy.
- For each tower that Umbra blows up, build an Archmage or Crossbow Fort to replace it. You want your money to turn into DPS in the most efficient way possible. Save your gold: buy very limited upgrades and only those capable of directly hurting Umbra or needed to save you from being overwhelmed by Shade Elementals. Barrage, Critical Mass, Wasp Missile and Death Rider are the only upgrades recommended.
- Sometimes, Umbra will destroy a weak tower. Keeping a few low-level Barracks or Archers there would somewhat increase this chance, potentially saving you a good tower.
- Melee heroes can hurt Umbra, and the boss cannot fight back except with the occasional lightning bolt used both to destroy towers and harm units, which is not enough to kill a durable melee hero like Alric or Grawl. Take advantage of this, send your melee hero to Umbra will allow him/her to deal a bit more damage to the boss. Take note when your hero is low on health to retreat safely - continuous combat with Umbra seems to increase the chance of the hero being targeted by the lightning.
- Nivus is always prioritized by Umbra: the poor old man will almost always receive a shot from the boss every time he respawns, and will most likely be killed instantly due to his low health. Thus, it is not recommended to use him in this stage.
- Any hero with less than 250-300 HP is susceptible to 1 shot kills from both Lord Malagar and Umbra, so it's ill advised to use them in this stage.
- Always pre-build a few Assassin's Guilds to guard the sidewards paths. Not only they are useful in resisting the previous 15 waves, they can keep Shreds of Darkness and Shade Elementals busy. Even though Knights Barracks work nearly as well without costing as much, you would want Assassin's Guilds so as to hold the Shreds of Darkness for as long as possible, since the high damage of Shade Elementals would burn through the health of Knights and even Templars rather quickly.
After wave 15:
- Pathetic! (after killing Lord Malagar)
- Now I'll consume this world!
- Now I'll consume this world!
- I'm not afraid of the dark, the dark is afraid of ME
- This is going to be legen (wait for it) dary!
- I'm every nightmare you ever had!
- I am a God, you dull creature
- 1,2,3, Umbra is here!
- Shadows betray you because they belong to me!
- I am invincible!
- Bwahahahaha HA HA HA!!
- You're not afraid of the dark, are you?
- Welcome to your doom!
- I'm not bad i'm just drawn that way
- Humans are a disease, I am the cure!
- The darkness, for me, is where I shine!
- Kneel before Umbra!
- One, two, Umbra is coming for you
- Resistance is futile!
- You and your friends are dead!
- Do you smell it? The scent of fear?
- I'll tear your soul apart!
- Why do you live?
- After the end credits, the corrupted Tear of Elynie is picked up by a monster with green hands and suction cups at the fingertips, saying 'Mine!' in the Futurama alien script.
- In the Heroic Challenge and Iron Challenge modes of Emberspike Depths, Vez'nan's staff and the Hammer of Ages are scattered around the area, the Hammer of Ages seen in the top left-hand corner near the crystals, and Vez'nan's staff seen near the west cliff.
- Umbra means shade or shadow in Latin.
- Umbra actually splits into 11 Shreds of darkness after the first time he dies, then 7 shreds of darkness on the second time, then 4 shreds of darkness on the last time.