After playing Undead Mode a few more times, ideas for Undead Mode in CtC3:

Stats of best combo per round
Stats of # of projectiles tossed per round
Bonus for perfect health at the end of the round
Terrain changes?
Defensive bonus options (moat, etc)
Napalm and bomb projectiles, but paid per shot ($100 per napalm, $150 per bomb)

Obviously you don't want to copy every other "base defense" game out there, but there are definitely ways to increase the playability of Undead Mode with just a few small changes, in my opinion.

Good, SquallLine! Actually, I don't like the Undead mode a lot, but with these changements, it would be funnier!

For the campaign mode (adventure), I would like changements. For example, upgrades by crushing castles and unlock weapons only in this mode.

In the Castle Builder, it would be nice if we can add water (lakes, rivers...).

In a comment made by Trismegistus about "Bendable Elements".  Knowing flash as little as I do, this would be very difficult to code albeit a nice feature.  If you look at the elements, especially the fixed elements like the stairs, you will see that they are actually squares.  In fact, every element is in the form of a rectangle.

It would still be nice to make the shapes a bit different in order to make arches (ie - trapezoid) and as well, have a colour chart to select different colours for the elements.

Water would also be nice for moats.

Another feature which I believe is available in Demolition City is to limit the number of each type of weapon you have available to crush the castle!

Joey's next project is Tower Defense which I believe is one where you build the castle and he tries to crush it....  Interesting concept...

What if you could fire spawn-bombs? You fire a big bomb who spawn when mouse-click to many bombs!

Another feature which I believe is available in Demolition City is to limit the number of each type of weapon you have available to crush the castle!

Yes, that's cool too.

I was thinking about a new type of blocks: the elastics blocks. When you launch an ammo as stone or log, it doesn't move and it throw back your ammo. It could be destructable only with fire or ice.

What if it is GIANTS as characters? They can stand against stones and log.

Yeah, JohnGarell, nice idea. Actually, it's too easy to kill them; if they was mode resistant, it would be funnier!

A NEW WEAPON:
a fireball: Such big as the BFR but on fire.
Or maybe 3 little fireballs if you throw them, they let a trace of smoke behind them.
They can destroy castle pieces but also destroy wood by burning it.

I see that lot of people like my idea of moats filt with water to create lakes.

Yes, but it looks like the fire.