Despite the low price ($2), probably one of the best Tower Defense games for the iPhone is Sentinel by Origin8. The title is highly popular; no wonder a sequel has just been announced, slated for June. I highly recommend it - apart from the repetitive in-game music, it's excellent. If you've ever played Tower Defense games, you already know how this one works. Therefore, I don't elaborate on the basics of the game (purchasing, placing, upgrading and selling weapons). Instead, I concentrate on real-world tips for surviving as long as possible. (Maximizing) Score The scores you get depend on mainly two factors: - Base Bonus: this score depends on the state of your final, base, third gate. By default, you get 5000 points at the end of every wave if it's intact (there's no currently any damage done to it). If it needs repairing, you get far less (in general, under 2000) points. - Barrier Bonus: this depends on how many of your additional gates are still intact. If both, you get (up to) 20000 points each wave, if only the second gate is intact, you can get (up to) 10000 points. If there's any (even the slightest) damage dealt to the gates, at least 5000 points are subtracted from this figure. What does this mean? 1. While it's certainly easier to comparatively easily let your first gate be destroyed around wave 35-40 by, for example, not backing it up with Beams, the additional several thousand points each wave can become a game-changer in, say, whether you can get onto the worldwide highscore chart. That is, if you stack up a lot of weapons to defend your first gate comparatively early in the gate (and, this way, you don't let your money stack up because of the high interest rates) instead of just relying on the (cheaper) weapons distributed along the long way to the second gate, you lose some money but gain a lot of additional points. 2. If the enemies deliver any damage to the gate early in the game (most importantly, the Arachnids are the most dangerous in this respect), try repairing them as soon as possible by purchasing the droids (or, at least one of them). This will result several times 5000 more points. Weapons Laser (20 / 20; 1/2/4/10; the meaning of these numbers: original price / upgrade price [which is the same as the original price, except for Slow]; original strength / strength after the 1st / 2nd / 3rd upgrade): the cheapest weapon. At first (at least until wave 10) it alone is able to stop attacks without the enemies dealing much (if any) damage to your first gate. In mid-game (in Medium level, over 60-70 waves), it's not worth purchasing any more as the maximal damage it deals, when fully upgraded, is 10 only. However, before that (particularly before wave 40-45; after that, it's worth gradually switching to Beams), it's probably the best weapon against flying creatures (Winged Parasite). Bomb (15/ 45 / 80 / 120): by far the most cost-effective weapon against weak ground enemies teamed up, particularly the very fast insects (Arachnids) and, to somewhat lesser degree, Mutants. Even usable in late game (over 120-150 waves in Medium level). I've found it far more cost-effective than even the two high-end weapons, Beams and Snipers. Make sure you keep at least 3-4 of them on your map even in late game. Slow (100 / 50; 20/25/30/35): you'll want to use these weapons to greatly slow down your ground enemies. A must to use against the main bosses (coming every 30 wave), the Warriors, to slow down their movements and keep them in the range of your most powerful weapons. Note: there is one weapon race that are not only immune to the slowdown effect of this weapon and, in addition, the Duo-Cranium Mutants. Therefore, you might want to do some micromanagement, particularly in late game where they have much bigger chance to get to the gate(s) and deal high damage to it if there's any Slow weapons on the map. That is, once you see there are Duo-Cranium Mutants coming, pause the game and quickly remove the Slow weapons from the map. As soon as another type of a ground enemy follows, just place them back. Given that these weapons are considerably cheap, you'll only lose 20% of their price ($20) when you sell one of them. This also means - as long as you use this kind of micromanagement - there isn't much point in upgrading them unless you have tons of money as, then, you'd lose more. Of course, you won't necessarily want to use this micromanagement as it takes a lot of additional time. Or, only remove few Slows, not all of them. Decide accordingly: there may be cases when you don't at all need Slows to slow down Arachnids or Mutants because your weapons get rid of them without problems. In the sample game below, I extensively use these kind of micromanagement. Ion (150 / 150; 30 / 90 / 150 / 230): one of the best weapons, which can be used even in early game (from about wave 20). As with Bombs, it delivers splash damage. In addition, it makes every creature going through its slow-burning fire lose heath for quite a long time (about 4-5 seconds with turned on fast mode) with sustained damage. That is, it's worth putting more of them on the map separated so that the enemies are always affected. Beam (250 / 250; 400 / 900 / 1400 / 2000): the most effective weapon. Interestingly, it's both faster and cheaper than the most advanced weapon, Sniper. Compared to the latter, it also has a slowdown effect (but not as long as that of the Slow weapons). The only disadvantage of them, compared to Snipers, is the reduced range. Sniper (300 / 300; 300 / 700 / 1100 / 1800): it's possible you can pass further in the "survival" mode if you go for these weapons exclusively instead of Beams - at least this is what is the screenshot HERE, which shows the player to have got to wave 285. [/IMG] It's not known at which level (Easy? Medium? etc.) he did so, though. Sample game Let me present you a sample game, with all the screenshots and the explanation of what I've done. Note that I haven't presented a screenshot of several waves; the simple reason for this is that I haven't bought / sold / upgraded anything during them. I started putting two Lasers on the both sides of Gate 1; of the initial $50, $10 remained. In Wave4 (of Arachnids), I've purchased another Laser and updated it at the same time. I've done the same to the two other, existing Lasers. In addition, I've bought a Bomb and placed it in front of the gate, making sure its range still includes the gate.