4) Scum off the earth:
* Mine. To mine forever, corrode your pickaxe by hitting a jelly, bless it. It is now cheap to repair by dwarven smith. Mine while having si in inventory for enough cash. Unlimited ore, with gemology skill gems too. Also generates stone giants, kill and eat corpse for possible +St. (Hardly scummy)
* ID Stair-hopping. Go up-down between two levels for quick items.
* Negative piety bug abuse. Make your deity very very very angry with you by repeated praying...suddenly all this negativity turns to super-positive piety. Use for a lot of precrownings, for example. You need to be able to survive the diety's energy bolt and summons. Dealing with summons can be done by making a wall of locked doors around yourself while standing on ID stairs. When done "summoning", just leave the level forever.
* Stat-gains. Basic idea is lowering stats to make it easier, or indeed possible to advance them. Sickness is known, as it lowers all stats. Starvation is much better, but works only on St, Le, Dx and Wi. Certain items give - to stat, like the common orcish helmet, -1 or -2 to Pe. More notorious is the ring of weakness, auto-cursing ring. It will set your St to 2 (cursed, 4 uncursed and 6 blessed). At this low St you will easily gain +St by eating corpses, or indeed walking around burdened. Corruptions also lowers stats and make them eligible for training. When corruption is removed, stat reverts to higher level.
* Experience-scums. Lowering the PC's speed when delivering a killing blow will increase experience gained. Lower speed by: Strained(!) status, Bloated status, Slow monster on self, wearing boots of slow shuffle. Also it has been said that turning the monster invisible helps too. There is also the "wish for emperor moloch in barbarians glade"-scum, wish on east side then teleport to safety across water. Now cast bolts or shoot missiles in total safety. Wishing for AKW when invisible is also pretty safe, you need to bolt (magic missile or wand of far slaying) him to death. Far slaying wand in a small room while wearing a AoLS, slowed, is a sure awy to gain a lot of levels (usually done after wish engine)
* Ultra healing potion scum. You need to take village elders' carpenter quest. Whenever the PC heals a monster, Jharod will either increase 'healing' skill dice, or (when skill is 100) give a blessed potions of ultra healing. These potions can be drunk for +1-3 permanent HPs. Heal monsters with 'cure x wounds', book-casted for unlimited. Monsters must not be hurt by PC, so a pet or alarm trap can be used. Generate monsters quickly with (book-casted) summon monsters spell, and the PC can quickly become "super-hardy"
ADOM General's warning: Treasure Hunting causes slowness, frailty, terrible markmanship and is dangerous to your characters' health