Balarama was laughing (prahasya) because He thought, “Krishna never cares to play with Me in My form of Sesa Naga, but now He is playing with this common, mundane snake named Kaliya.”
Remembering Krishna’s pastimes as an ordinary mortal, Balarama smiled and said nothing though the situation was beyond tolerance. However, when Balarama smiled the Vrajavasis forgot their fear and lamentation and felt that nothing unfortunate would happen. Filling with the joy of Balarama’s smile, they no longer desired to give up their lives. (16.16)
However when Krsna appeared as Lord Caitanya , He did play with Lord Ananta Sesa that took a form similar to a snake , Lord Ananta in ancient times did tapasya to enter Sri Navadvipa Dhama . . Lord Ananta wanted the darshan of Sri Sri Radha Krsna and asked Lord Visnu how it would be possible, Lord Ksirodaksayi Visnu told Him that it was not possible unless He did tapasya in Sri Navadvipa , so later when Lord Caitanya appeared in Sri Navadvipa Lord Ananta saw the combined form of Radha Krsna , Lord Caitanya .Sri Krsna Caitanya ,Radha Krsna nahe anya ...this is explained by Srila Bhaktivinoda Thakura in his Navadvipa Dham Mahatmya ,Pramana kanda /
Srila Bhaktivinoda Thakura writes in his Caitanya lila smarana mangala stotram :
sarpakatim svanganam hy anantam
katvasanam yas tarasopavirtah
tatyaja tam catmajananurodhad
visvambharam tam pranamami nityam
sarpa—of a serpent; akatim—form; sva—own; anganam—courtyard; hi—certainly; anantam—Lord Anantadeva; katva asanam—sitting; yah—who; tarasa—quickly; upavirtah—seated; tatyaja—abandoned; tam—him; ca—and; atmajana—of the relatives; anurodhat—because of consideration (or because of the appeals); visvambharam—to that Lord Visvambhara; tam—to Him; pranamami—I offer my respectful obeisances; nityam—repeatedly.
When Lord Anantadeva assumed the form of an ordinary snake and entered [Jagannatha Misra’s] courtyard, young Visvambhara immediately began to play with Him. When the distressed relatives appealed to Him, Visvambhara went away from the snake. I repeatedly offer my respectful obeisances to that Lord Visvambhara.
In the Narayana Kavacha it is mentioned that Lord Anantadeva protects us from envious humans beings
dhanvantarir bhagavān pātv apathyād
dvandvād bhayād ṛṣabho nirjitātmā
yajñaś ca lokād avatāj janāntād
balo gaṇāt krodha-vaśād ahīndraḥ
Word for word:
dhanvantariḥ — the incarnation Dhanvantari, the physician; bhagavān — the Supreme Personality of Godhead; pātu — may He protect me; apathyāt — from things injurious to the health, such as meat and intoxicants; dvandvāt — from duality; bhayāt — from fear; ṛṣabhaḥ — Lord Ṛṣabhadeva; nirjita-ātmā — who fully controlled his mind and self; yajñaḥ — Yajña; ca — and; lokāt — from the defamation of the populace; avatāt — may He protect; jana-antāt — from dangerous positions created by other people; balaḥ — Lord Balarāma; gaṇāt — from the hordes of; krodha-vaśāt — the angry serpents; ahīndraḥ — Lord Balarāma in the form of the serpent Śeṣa Nāga.
May the Supreme Personality of Godhead in His incarnation as Dhanvantari relieve me from undesirable eatables and protect me from physical illness. May Lord Ṛṣabhadeva, who conquered His inner and outer senses, protect me from fear produced by the duality of heat and cold. May Yajña protect me from defamation and harm from the populace, and may Lord Balarāma as Śeṣa protect me from envious serpents.
To live within this material world, one must face many dangers, as described herein. For example, undesirable food poses a danger to health, and therefore one must give up such food. The Dhanvantari incarnation can protect us in this regard. Since Lord Viṣṇu is the Supersoul of all living entities, if He likes He can save us from adhibhautika disturbances, disturbances from other living entities. Lord Balarāma is the Śeṣa incarnation, and therefore He can save us from angry serpents or envious persons, who are always ready to attack.