When using Potion, can I choose to heal less than 30 damage from my Pokemon?
If the Pokemon has 30 or more damage on it you must heal 30 damage, but if it has less than 30 damage you do as much as you can and heal all of it.
Source: TPCi Rules Team (2017-05-18)

Relevant cards

Note: All applicable cards may not be listed below.
WOTCB1_94
WOTCB2_122
WOTCB2_122
BW1_100
BW7_132
DP1_118
DP3_127
DP7_92
EX1_91
EX10_95
EX11_101
EX14_87
EX6_101
SM1_127
SWSH1_177
SWSH1_177
TK10-Raichu_15
TK10-Raichu_15
TK1-Latias_8
TK1-Latios_8
TK2-Minun_10
TK2-Plusle_9
TK3-Lucario_9
TK3-Manaphy_11
TK5-Excadrill_15
TK5-Excadrill_15
TK5-Excadrill_23
TK5-Excadrill_23
TK6-Noivern_15
TK6-Noivern_27
TK6-Sylveon_20
TK6-Sylveon_24
TK7-Bisharp_25
TK7-Bisharp_25
TK7-Bisharp_29
TK7-Bisharp_29
TK7-Wigglytuff_15
TK7-Wigglytuff_15
TK7-Wigglytuff_20
TK7-Wigglytuff_20
TK8-Latias_15
TK8-Latias_15
TK8-Latios_21
TK8-Latios_21
TK9-Pikachu_21
TK9-Pikachu_21
TK9-Suicune_15
TK9-Suicune_15
WOTCE1_156
WOTCLC_110
XY0_37
XY12_83
XY9_106