Well the Hanso Charisma Charm, Ghostkerbomb, and Randomly Firing Freeze Ray are all good investments to make if you are looking for items that will retain their value
and usefulness.
I also recommend getting some Anagram Swords; Sword of Reif and Kelpbeards Trident specifically.
With the release of the Sword of Tawre I have a sinking suspicion that the Kelpbeards Trident will soon be retired as such investing in it is safe either way because it is very unlikely to deflate and if it does go retired it will inflate at a healthy rate
For the healing end it is a bit harder to say, Greater Healing Scroll is the most cost effective way but it is hard to predict the market on those.
For freezing I recommend investing in Magical Marbles of Mystery as you really can't go wrong with those a dual duty 100% freezer that is going to retain its value.
Downsize is a Once Per Battle 50% blocker, Thick Smoke Bomb is a One Use 100% blocker... I prefer using the Thick Smoke Bomb myself, an entire turn to smash my opponent is great. Since the Thyoras Tear is running 65mil+ I prefer the cheap effectiveness that the Thick Smoke Bomb offers.
If you are looking for cheaper investments they are much harder to make because when new weapons and armor is released it is normally with lower icons and consequently cheaper because of it. If you buy a lot of Rainbow Scroll's more being released are going to hurt your investment, a different mass released weapon that does the same/similar icons will likely cost less and sell faster, and ultimately it is too unstable a market on the lower end of the Battledome to effectively surpass the flaws of investing in those items.
Edited by Yung, 17 January 2012 - 04:33 PM.