Data acquired from a few days of reloading save states in PocketNES, and keeping track of every result. Fights were mainly vs Metal Babbles in Sacred Tomb.

0.30%All Allies Agility goes up1/370
0.30%Chance echoes, no other effect1/370
0.30%Return to random town1/370
0.80%All enemies and allies are put to sleep3/370
1.10%All Enemies and all Allies MP reduced to 04/370
1.60%Chaos on all Enemies and all Allies6/370
1.60%Earthquake! All Enemies and all Allies take ~60 damage6/370
1.90%Blinding Light: 80%-150% of max hp in damage to caster7/370
2.20%All Enemies and all Allies build up power (x2 next turn)8/370
2.70%Allies Morale is boosted (Crit rate goes up)10/370
2.70%Healall all Allies10/370
3.20%Caster calls Most fearful thing, Allies faint, Enemies run12/370
3.50%x2 XP & Gold at end of battle (though it only says money)13/370
4.10%Earthquake too! All Enemies die (XP given)15/370
4.90%Bedragon on all Allies18/370
5.10%Time Stops, only caster acts for 3 turns19/370
5.40%Hideous Grumble heard, Allies lose a turn20/370
5.40%All Enemies explode into bits! (No xp earned)20/370
5.40%Monstrous Giant laughs and attacks all Enemies for ~11020/370
5.90%Blinding Lights; White Dragon kills all Enemies (no xp)22/370
6.20%Surround on all Enemies23/370
7.00%Time regresses 1 turn (As Sandglass of Regression)26/370
7.60%All Enemies turn into Metal Slimes28/370
7.80%Eerie mists stream out of caster (Fendspell on all)29/370
13.00%All Allies Defense goes up (Upper)48/370