PTD: General Tips
Keeping Track of the Battle
While it is so easy to expedite combat by pressing on the 4x speed up key, you will not be able to keep track of the battle this way. After all, you also need to see which attacks are effective, which need changing, and more importantly, if an enemy can be caught in your Pokeball. When leveling up your troops, changing their attack behaviors and choosing positions (like when you decide to change your strategy), it is best to slow the game down.
Speeding up the game is great when you are already sure of your defensive plan. Whether you are just farming credits or blindly leaving your Pokemon to level up, maxing the speed is a great way to lessen the time you need to spend. However, do note that if a Pokemon does level up, you should spend the necessary credits to raise their levels - they will not gain further experience points until you do so.
Of course, it goes without a saying that you need to keep an eye on the enemy target - which is usually candy, but in some cases, containers and even PokeBall. The goal of these Pokemon are to take and steal these things. This means that for the most part, you have a chance of beating them either on their way to the candy, or when they try to carry it out.
Letting the enemy grab some candies is not a good thing, but sometimes it can work to your advantage, you just need to know how. The thing about enemies is that once they grab a candy, they will move towards their exit. If the candies (or any other target) are placed in a hard to defend location, you can let the enemies get to them, have the key items dragged out and when the enemies are near a better defended location, you defeat them there and the candies will be dropped down. Note that this strategy is only good for moving the target items, it will not change the route of the enemy - they will still charge towards the original location of the candies.
Attacking: The Other Side of the Game
Pokemon Tower Defense is entirely all about fending off other Pokemon, there are also some stages where the goal is for you to charge in and attack. In these stages, a set number of enemy Pokemon will be standing guard waiting for your troops - and this is where all those defensive abilities will come in handy. Now, if you have overwritten all the defensive skills, worry not. You can spend 1000 credits to change their skills by using the relearn feature. This will enable you to access any old skill that you did not include in their 4 active abilities. Naturally, abilities that increase defense, evasion, movement speed, nullify attacks and reflect abilities are very important (yes, even skills like Teleport become really handy at this point).
The important thing to remember when you are attacking is that the movement of the Pokemon vary. So if you want Raichu (who moves fast) to go in front of Nidoking (who moves a bit slower), you will have to summon Nidoking first, let him gain a bit of headstart, then follow up with Raichu who will easily overtake him. If you send Raichu out first, the distance between the two will be so far that you might as well have sent them out separately. This slow and fast combination is a good idea for getting towers to attack your slower, tougher Pokemon while a faster one sneaks past them all. Also, it is not always a great idea to clump Pokemon together. Be wary that some towers will use area of effect attacks that will damage several of your Pokemon in a single hit. Also try to bring some creatures that can remove negative status ailments along for the attack.