Likely little. As @Torisuda has mentioned, there's no incentive for them to create pokemon that toe the line - it's a show for kids, they will want innocent monsters.
- Sexual content/innuendoes
A definite no go area for a kids show
- Violence (gore, mutilations, etc.)
Considering pokemon only 'faint' and there is purposefully no death in the series, this isn't an issue in character design.
The only complaints have been at the presence of fighting creatures from animal and religious groups. But even this is unwarranted - in 2000, Pope John Paul II gave his blessing to Pokémon and said it did not have "any harmful moral side effects"
You could draw parallels with pokemon and Shinto, but the show is pretty much ignoring religious references, and quite rightly.
- And others (offensive language, stereotypes, political matters, etc.)
There is one instance I can think of this, In Western editions, Jynx is purple-skinned rather than black, as it is similar to blackface:
Most censoring is done before a show hits the market, so if there are more instances, they're probably known only by the production crew - and kept secret.
There are definitely discarded creatures, but mostly because they were removed for quality reasons. Some of these made their way into later versions of the series (like Ho-oH) and some were simply redesigned.
At a fan convention in 2010, Shigeki Morimoto (the lead programmer of the first Pokemon games) confirmed that there were originally 190 Pokemon intended to be included in the release of the First Generation of Pokemon games. This is backed up by the fact that for the first 190 of the 255 slots in the hex grid of Pokemon, all slots possess either a valid Pokemon, or the same form of Missingno. All 191 slots and later contain garbage data that produce different glitch Pokemon in each slot.