Some generic tips:
- POWs, I don't know why people classify it as useless. They are great for stripping items away from players. I tend to fire them at the same time as with a Shock: once everyone else in front of me got their items. If the road to the next item line is long and you get a good item right after, chances are you will turn the tables dramatically. I'm still learning how to use these personally.
Of course, if by the time you fire you can strike a few players that are performing a tricky turn, the better.
- Abuse Green Shells more effectively by touching a speed booster or doing a Mini-Turbo and then fire these. The faster the vehicle, the faster Green Shells go. This tip is kinda limited in usefulness because not every track has speed boosters and aiming right after a MT is hard (not much for Karts though). Also, they slow down after a while so it's best used for a close-range surprise attack or killer ricochet ambush.
- In Battle I find using Bombs as 1-second Shields to be rather amusing. Hard to use them this way though (drop a Bomb then reverse into it to explode and destroy incoming Shells).
- Time your Blue Shell attack so that it hits the leader after it crosses an item line. If you know the leader has spare Mushrooms, time the Blue Shell so that it hits him just before a tricky turn or just before an important shortcut in an attempt to force the player to go wide and lose time, or mess up and slow down.
- The farther you move on before using a Bullet Bill, the better. Bullet Bills won't stop until they reached the maximum flight time or whenever they have passed 2-4 players (2 for 4 player rooms, 4 or maybe 5 for 12 player rooms), so move as high as you can before using it.
Ideally, the best position to use Bullet Bill would be 5th (12P situation), with 1st place like 8-11 seconds ahead of you. I can't help but imagine the user scoring a Shock dodge and the 1st guy getting Blued during the process, LOL...
That's all I can think of. I was writing a Item Book myself but eventually lost inspiration, however your guide can prove to be useful. Keep up the good work!